Image source, Getty Images

Former President Joe Biden, who is present today at the memorial in New York City, shared some words on social media honouring the victims and first responders killed on 11 September.

"This morning, Jill and I hold close the families who carry that loss every day. We honor the heroes of September 11th: the firefighters and police officers who rushed into the towers and the Pentagon, the passengers who fought back over Shanksville, and the generation that stepped up to serve in the aftermath," he wrote.

Hillary Clinton, the former US secretary of state, said "the consequences have continued for 25 years", and it's our job to inform younger generations who are too young to remember the attacks.

"Something worth remembering 25 years after 9/11: in the aftermath of catastrophe, people look around, they see what is needed, and they help," she wrote online.

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Former New York City Mayor Eric Adams has also spoken out.

"Cowardly terrorists stole all of that in an act of pure evil. They murdered innocent people and left families with a pain that no anniversary can erase," he said. "As a New Yorker and a former NYPD officer, this will always be personal to me."

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Surrounding the memorial pools and the 9/11 Museum are approximately 400 swamp white oak trees, a species native to all three crash sites from the 2001 attacks in New York, Arlington, Virginia, and Shanksville, Pennsylvania.

They form a calm space in the heart of downtown Manhattan and provide welcome shade during New York's fierce summer heat.

There is also one tree different from the others - a Callery pear tree - that was discovered severely damaged underneath the rubble in October 2001. New York City's Parks and Recreation Department removed it from the site and nursed it back to health.

The tree was then replanted at the site of the World Trade Center as a symbol of resilience and perseverance.

Nearby, an open space among the trees - known as the Memorial Glade - is dedicated in honour of those who are sick or have died from exposure to toxins in the aftermath of the attacks, including first responders, survivors and volunteers. They will be remembered today with a new seventh sounding of a bell and a moment of silence.

Image source, AFP via Getty Images

Marcy Borders became the subject of one of the most enduring images of the 9/11 attacks.

She was just one month into a job at a Bank of America office on the 81st floor of the North Tower when a plane hit it.

"The building started quaking and swaying. I lost all control, and I went into a frenzy. I fought my way out of that place," Borders later recounted.

Defying instructions from her boss to stay put, she fled down the stairway and into the lobby of an adjacent building where she was photographed by Stan Honda, a photojournalist at the AFP news agency.

Covered in dust, her shell shocked face was emblematic of the nation's mood. In the media, Borders became known as the "Dust Lady".

Following the attacks, Borders suffered from severe depression and addiction. She died in August 2015 from stomach cancer, one of the most common cancers diagnosed in 9/11 survivors.

"Not only is she the 'Dust Lady' but she is my hero and she will forever live through me," her daughter Noelle Borders said following her death.

As you will have seen from our coverage today, every year on 11 September, bells ring to commemorate the exact time that each of the four planes crashed, and the exact time that the Twin Towers fell.

Each of the six bells is followed by a moment of silence.

This year, a seventh bell will ring. Its purpose is to commemorate the thousands who died from diseases including cancer after the attacks.

Illnesses related to dust and smoke from the towers' collapse have since claimed more than threefold the nearly 3,000 lives lost in the attacks, US health officials say.

“As the years pass and the human toll grows, we reckon with the cost of September 11th whenever another New Yorker is stolen from us too soon,” New York City Mayor Zohran Mamdani has said. “Now, close to 25 years later, more people have died from 9/11-related illnesses than were killed on the day itself.”

Image source, Getty Images

The 9/11 Memorial covers eight acres of the 16 acre World Trade Center campus in New York. Dominating the space are the two large memorial pools set within a plaza of approximately 400 swamp white oak trees.

The design, Reflecting Absence, was submitted as part of an international competition by architect Michael Arad and landscape architect Peter Walker.

Featuring twin waterfall pools surrounded by bronze parapets listing the names of the victims of the 2001 attacks and the earlier 1993 bombing of the World Trade Center, they mark out the footprints of the two towers.

Covering about an acre each, they contain the largest human-made waterfalls in North America, each descending 30ft (9m) into a square basin where water continues to fall another 20ft into a smaller central void.

The memorial opened on 11 September 2011, ten years after the attacks

Image source, Getty Images

Commerce Secretary Howard Lutnick, who is at the New York memorial today, is honouring his brother, Gary, who was killed alongside many of their colleagues at Cantor Fitzgerald's offices at the top of the North Tower of the World Trade Center.

Lutnick says his brother Gary was "the kindest and most fun person I knew".

"Gary was happy in every photo. Over the past 25 years, nearly every day there has been a moment when I’ve thought to myself, I wish Gary was here," Lutnick says.

"Gary was killed at the young age of 36 for being an American and going to work that morning in the greatest country in the world. I love and miss you every day, my brother," he adds.

Cantor Fitzgerald accounts for the largest loss of life of a single organization during the attacks, with 658 employees losing their lives.

Image source, Getty Images

We're continuing to show you some of the other ways the city commemorates the victims of 9/11 and how these memorials have reshaped the city's architecture:

In Liberty Park, in an elevated garden overlooking the 9/11 Memorial, stands the heavily dented black and gold Koenig Sphere, which once sat at the heart of the original World Trade Center development.

The 25ft (7.5m) tall cast bronze sculpture weighs 25 tonnes and was originally commissioned in 1966 as a centrepiece for the plaza between the towers.

The work of German artist Fritz Koenig, it was dedicated to “world peace through trade” and was the largest bronze sculpture of modern times.

The sphere was the only work of art recovered from the rubble after the 9/11 attacks. It was dismantled and stored before being relocated to Battery Park in 2002, then moved to its current position in 2017.

Image source, Getty Images

Memorials are continuing to be held across New York City today as the city commemorates those who died on 9/11.

Here's a look back at what we've seen in the last 24 hours:

Image source, Getty Images

Image source, Getty Images

Image source, Getty Images

Image source, Getty Images

Tom Brook
Presenter, Talking Movies

BBC presenter Tom Brook was part of the New York news bureau in 2001 and recalls with admiration how a colleague dealt with the loss of his brother in the attack on the World Trade Center.

On 11 September, 2001, I was in Canada covering the Toronto International Film Festival. With us as part of our small BBC Talking Movies team was Andrew Rice, a very gifted and likeable video journalist. His 31-year-old brother, David Harlow Rice, worked for the investment banking firm Sandler O'Neill on the 104th floor of the South Tower of the World Trade Center. He was one of more than 60 employees from the firm who died that day.

In Toronto, I remember the agony Andrew experienced endlessly calling David’s mobile phone and just getting voicemail. I felt pretty helpless trying to comfort him. They found his brother’s body pretty soon after he returned to New York a day or so later.

Looking back, I take great inspiration from how Andrew responded to his brother’s death. It wasn’t all smooth sailing, but he left Talking Movies and New York and returned to his native Oklahoma, got married, and then got elected as a state senator. He served for six years. He's gone on, by all accounts, to live a very full and productive life - a life which has been characterised by a healthy concern for injustice.

Now I work out of the BBC News bureau in New York, close to the World Trade Center site.

Every time 11 September comes around I think of Andrew and I admire his strength. He ultimately dealt with the horror of 9/11 in generous, intelligent and life-affirming terms. That he was able to do this serves as a great example to us all. It will always inspire and stay with me.

Earlier today, President Donald Trump gave remarks at the Pentagon during the 9/11 ceremony held there. On 11 September 2001, American Airlines Flight 77 struck the US military headquarters, killing 184 people in the building and on the plane.

Trump was joined by several members of his Cabinet. Condoleeza Rice, who was secretary of state at the time of the attacks, also gave remarks.

Image source, Getty Images

Image source, Getty Images

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Image source, Getty Images

A few minutes ago, we heard from Stephen Evans - a former BBC North America business correspondent - who was reporting from New York when one of the Twin Towers collapsed behind him.

He describes feeling "real terror as the debris came towards me", thinking for a moment: "It's coming faster than I can run."

He says that day "felt like an attack on all of us" and he describes strangers hugging in the street. He says people were angry "collectively" on behalf of "what felt like the world".

As a reminder, we also heard from Evans earlier, when he described waiting for a meeting on the ground floor of the South Tower when the first plane hit the North Tower.

Reflecting on that moment again now, he describes "still winc[ing] at the sound of that plane".

Image source, Getty Images

As the 9/11 ceremony in New York continues, we're going to show you some of the other ways the city commemorates the victims of the attacks throughout the year:

The 9/11 Memorial Museum documents the 2001 attacks and the 1993 World Trade Center bombing through artifacts, photography, video, personal stories and interactive exhibits.

Visitors enter through a pavilion, but the bulk of the museum is beneath the ground where architects designed spaces that showcase remnants of the site including the Survivors’ Stairs which led hundreds of people to safety during the attack.

At bedrock, in two monumental spaces, largescale artworks remembering the victims are on display in addition to a huge portion of the concrete retaining wall that was built in the 1960s to hold back the Hudson River.

The museum also has two galleries of rotating exhibits. Two of the most striking artifacts are a partially crushed fire truck and the “last column”, the final piece of steel removed from the site as it was cleared.

Image source, Getty Images

If you've been watching our livestream of the memorial ceremony in New York you will have seen many parts of the National September 11 Memorial and Museum which occupies the site of the original World Trade Center.

We're going to show you how the various elements of the memorial - including the museum, the Survivor Tree and Memorial Glade, the South and North Pool as well as the Performing Arts Center - pay tribute to those lost that day, the first responders and volunteers, and those grieving their loved ones.

Nada Tawfik
Reporting from New York

Image source, EPA

Today’s ceremony, on this pleasant morning in Manhattan, has been a renewed promise to never forget the pain and loss of 9/11.

A quarter of a century on, families and first responders have gathered in solemn remembrance and kept alive that poignant tradition of reading the names of the nearly 3,000 men, women and children killed.

Nearly a third of the country is now too young to remember 9/11 – experiencing it only through heartbreaking testimony and evocative videos - but there seems to be a firm resolve within the city to keep those memories, no matter how difficult, alive.

Paddy O'Connell

BBC radio and TV presenter Paddy O'Connell was based in New York in 2001. Here he recalls the events of 11 September and what came after.

It was a Tuesday, with clear blue skies. I never arrived for my meeting at the Twin Towers that day as I'd overslept.

For several hours we couldn’t call or meet each other. I feared my camera colleagues had died - thankfully they had not.

I was in the New York Stock Exchange when it re-opened six days later - there was a smell in the air like burnt meat mixed with petrol.

New Yorkers really came together. We were urged to hit the Broadway shows and clubs and restaurants to boost the economy. I did all of that.

Weeks later, I rang up a Wall Street banker for my reporting work, only to find out he’d been killed in the World Trade Center.

To this day, I refuse to watch the videos of the planes hitting the towers.

Image source, Reuters

Former Vice-President Kamala Harris and former President Bill Clinton have both released statements honouring the victims of 9/11.

In her statement, Harris notes that a generation has grown up in the years since 9/11, "but our responsibility to remember has not changed".

"We remember the people who went to work that morning and never came home, and we remember the families who have carried their memories every day since," she says.

Clinton says the country is remembering all those lost in New York, Virginia, and Pennsylvania. He also mentions all the people who have fallen ill from exposure to toxic materials after the building collapse.

Clinton says it is not possible to erase the nightmare of the attacks, "but we can support the people who have given and lost so much by treating one another with respect".

Kayla Epstein
Reporting from New York

Image source, BBC News

On Friday morning, John Ryan sat quietly in an office building across the street from the memorial, gazing through a picture window at the open sky where the Twin Towers once stood.

On his mind were the friends who died in the attacks - "all young guys": a fellow court officer, firemen, and a friend who worked in the World Trade Center at the financial services firm Cantor Fitzgerald.

“It was the day that changed the world. The day that changed my life,” Ryan, a retired court officer who had been visiting his brother in Connecticut on 11 September 2001, tells me.

“I wasn’t allowed to come back to Manhattan until that Friday,” he continues. “And the one thing I remember about Friday night, about 6 o’clock, they had a vigil.”

“That night, everybody stood still. All the cars stopped. Nobody moved. You know, Manhattan, they don’t stop for anything. For those minutes, everybody stood still.

“And the only noise is this plane flying over, and it was so quiet it just pierced the silence,” Ryan says, closing his eyes as he remembers events from 25 years ago.

Grace Eliza Goodwin
Reporting from New York

Back in New York, we just heard the sixth bell ring at 10:28 EDT, which marks the exact moment the North Tower fell on 11 September 2001.

The Oculus, a shopping centre that opened in 2016 near the 9/11 Memorial, was designed to resemble, on its exterior, a dove flying out of a child’s hands.

Inside, two long strips of windows cut into the ceiling above an oval-shaped passageway offer a glimpse into the sky above.

Every year on the morning of 9/11, these windows are designed to cast two beams of sunlight onto the floor below in honour of the Twin Towers.

“Here the Sun stands at 10:28 am on September 11, completing a wedge of light,” an inscription in the centre of the passageway reads.

The “Way of Light” as its called, is supposed to last from the time the first tower was hit to the time the second tower fell.

Today, however, on the 25th anniversary of the attacks, clouds are blocking out the light and no beams appear.

Trump ends his address by saying 11 September "reminded us of the terrible power of hate", but it also showed "the power of the American spirit".

"No one can ever prepare for a day like 9/11. But we can always choose to be the kind of nation the world saw in those days after," Trump says.

"We can raise our children to know that their country is good, that their fathers are brave, and that our flag is a symbol of justice and freedom."

With that, he concludes his speech at the Pentagon.

Iran war looms over Trump's speech at Pentagonpublished at 15:30 BST

15:30 BST

Bernd Debusmann Jr
White House reporter

Image source, Reuters

While he alluded to it before, Trump has now explicitly linked the war with Iran to the events of 9/11.

Since the attacks took place, Trump says, members of the military have "travelled to the darkest corners of the earth and done battle with a shadowy enemy".

It is clear the the spectre of the war in Iran is looming heavily over the administration as it marks the 9/11 anniversary.

US troops are still in harm's way overseas, and the US military remains heavily committed to the Middle East decades after US soldiers deployed to Afghanistan and Iraq.

Iran was among the countries described as the "Axis of Evil" by President George W Bush a few months after the 9/11 attacks, and his administration is known to have actively considered military action against it a few years later - but ultimately moved in favour of diplomatic pressure and sanctions.