The bands continue with their slow-paced tracks. Next up is "Merry Go Round", a psychedelic rock tune also from Arirang and a somewhat melancholy take on life.

"My life is a broken roller coaster, but maybe I'm the only one to blame, I do my best, but I can't slow down this merry go round," the lyrics go.

V opens their lead track in Arirang, Swim, which has been described as an alternative pop track in a slower pace.

BTS member RM, who is the group's main songwriter, said: "I wrote the lyrics and I tried to express the confusion that we all had before after the military and we want to just keep swimming."

Jake Kwon
Reporting from Goyang

Image source, Jake Kwon/BBC

Now that the show has begun, I can see more than a hundred fans outside the stadium listening in. They don't have tickets but are still here to be a part of this night.

There were some very unfortunate fans. I saw one lady panicking and breaking down in tears at the gate because she couldn't find her ticket.

Now it's on to one of their classics, the 2018 released Fake Love. It's the pop-rock song, about disappointed love - and it heroes Jimin and Jin, their vocalists.

They have just wrapped up another song from Arirang - "Like Animals" - which our music correspondent called "surprisingly carnal", given how chaste K-pop tracks usually are.

Mark Savage
Music correspondent

The rain is still pouring down in Goyang, causing a few technical issues in the stadium. The stage smoke that was supposed to create an atmosphere at the start of the show lingered in the air instead of dissipating, obscuring the view for some fans - especially those watching the livestream, where it looked like BTS were performing in the middle of a London fog.

But as the view clears, it’s clear the band are determined to battle the elements. So far, the show has forefronted their rebellious, rap side - opening with Hooligan, Aliens and a choppy, percussive version the fan favourite Run BTS.

And the band are full of energy. Even RM’s ankle injury seems to have healed, as he bounced around the stage despite the slippery conditions.

Jin continued to talk about the poor weather condition, saying that he hopes everyone will just have fun tonight.

"The most important thing is to make memoery with Armys," said Jimin.

"This will defintealy be unforgetable," J-Hope continued to say.

Jin then asked fans to put down their phones. "Let's just have fun," he said. "It will be against the rules if you lift your phones up."

J-Hope then asked people to scream once more, as they got ready for the next song.

Each member took turns addressing their fans.

"I was frustrated and stressed by the news that it'll rain today, but I don't think that the rain matters," Jimin said.

"The fact that you are here is important. if you could see us, it's all good."

"It's been four years", says RM, before Jungkook started talking about how hard they've worked for this moment to stand before their fans again.

Jin talked about the rain, saying the weather forcast suggested the rain would stop before the concert.

Suga then joked, "you can't believe the weather forecast".

RM ends the three first songs yelling "makes some noise". He greets the BTS Army with their signature move, where they all bow in unison as they say "Hi we're BTS".

"Long time no see," RM then said.

We can't use photos from inside this concert, but here's an earlier picture of their signature greeting.

Image source, Getty Images

BTS continues on with their third song, Run BTS. Even as it continues to pour, they groove along in the rain.

This is one of their older hits, which released in 2015, when they were still making a name for themselves. But the fast-paced high energy track remains popular.

Before today's show, there was speculation over whether the group’s leader, RM, who injured his ankle ahead of the group's 21 March performance in Seoul, would be able to fully participate in the choreography.

Now that we’ve seen him on stage without a cast, it’s an encouraging sign.

Fans will be hoping this means they’ll finally get to see the complete group choreography performed live in full tonight.

They continue on with Aliens, the third track on Arirang. Fans are chanting and screaming.

Image source, Hosu Lee/BBC

The show starts with their new song Hooligan. The group is on stage and fans are screaming!

Right before the concert, the excited fans were chanting each member’s name then shouting ‘I love you, BTS!’

We can now see a group of dancers, dressed in black and all masked, on stage. The seven members are also walking toward the stage.

“Everyone around me is already switching on their Army Bomb lightsticks, which really elevates the mood," says Park Su-bin, a wheelchair user in her 30s who is inside.

The biggest K-pop bands have their own lightsticks, and the BTS ones are purple, their signature colour.

Even though it’s been raining all day, fans are filling the stadium. Even the wheelchair-accessible seating areas seem to be full, Park says.

Mark Savage
Music correspondent

Just before showtime, the livestream has switched to a view inside Goyang Stadium.

We can see the massive, 360-degree stage in the middle of the stadium for the first time. It has four long catwalks shooting off into the audience, meaning everyone will get the chance to get up close with their idols.

Most of the fans are still wearing raincoats and ponchos, but the nightsticks are already aglow and anticipation is mounting.

Jake Kwon
Reporting from Goyang

It's minutes before the show - fans are now running. Some look panicked as they ask staff members for directions. Staff with light sticks and whistles are hurrying the crowd along.

Some have also been trying to profit from the concert by selling counterfeit fan merchandise – and that's kept South Korea's Intellectual Property Office busy.

The agency has deployed officers outside Goyang Stadium to crack down on peddlers. It has also set up a team to track counterfeit sales online, which is working to take down related listings.

Over the past two months, the agency says it has identified more than 25,000 counterfeit K-pop items online with BTS merchandise accounting for the largest share, followed by Stray Kids and Twice. It's also been running campaigns to help fans distinguish authentic merchandise from counterfeits.

Image source, David Dee Delgado/Getty Images