Air testing confirms 'no hazard exists' at Pentagon after lockdown incident

Normal operations have resumed at the Pentagon after the building was earlier placed on lockdown following the detection of an "air quality issue" that sent hazardous material (hazmat) response teams to the scene.

The building's systems detected on Thursday morning a "potential air quality issue, prompting immediate precautionary safety measures and evaluation", said Pentagon spokesperson Sean Parnell in a statement.

"Subsequent testing confirmed no hazard exists, and normal operations have resumed," he said.

Police in the building had been wearing gas masks and full chemical protective gear during the incident, US media reported.

The Pentagon was assisted by Arlington Fire & EMS, who posted on social media that they were responding to a hazardous materials incident.

Earlier, Parnell had said "standard protection protocols, including a shelter-in-place order for the affected area" of the building, where the US Department of Defense is headquartered, were in place.

Just before 11:00 EDT (16:00BST), the Pentagon Force Protection Agency sent an email to Pentagon personnel to shelter in place in four corridors from the second to the fifth floors, according to CBS News, the BBC's US news partner.

The email told staff to comply with the directive and move in-person meetings to virtual meetings, according to CBS News.

"We express our sincere appreciation to the first responders for their swift actions to ensure the safety of all personnel," Parnell said in his updated statement at around 13:30 EDT (18:30BST).

The Pentagon, located in northern Virginia just outside Washington DC, has more than 20,000 government employees working in the building.