The Pentagon has been locked down and staff evacuated with a hazmat team rushing to the US military headquarters over a 'hazardous materials incident.'

Multiple floors and corridors of the sprawling complex have been locked down and others are being evacuated, three sources told CNN. 

Firefighters in full protective clothing, including gas masks, were seen rushing inside the building in Arlington, Virginia, on Thursday morning.

Pentagon spokesman Sean Parnell confirmed that 'an air quality issue' had been detected, sparking 'precautionary measures until we determine its significance.'

'The Department is executing standard protection protocols, including a shelter-in-place order for the affected area,' Parnell said. 'Response teams are in place and ready to support building occupants.' 

Arlington County Fire Department posted on X: 'ACFD units, including our Hazardous Materials Team, are currently operating at the Pentagon in support of PFPA's Hazmat Team during a hazardous materials incident.'