Firefighters were investigating a hazardous materials incident at the Pentagon on Thursday, Arlington County fire and rescue officials said in a post on X.

The building was under ⁠lockdown with people evacuated from several floors, CNN reported, citing unidentified sources. It said emergency ⁠responders were wearing full gas masks and chemical protection suits.

"The Pentagon has sophisticated systems to ensure the safety of the building and its occupants. Those systems have detected an air quality issue necessitating precautionary measures until we determine its significance," Pentagon spokesman Sean Parnell said in an ⁠email.

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

Floors two through five were locked down, as well as some corridors, CNN reported.

The five-sided Pentagon building, hit during the Sept. 11, 2001, al-Qaida attacks is one of the world's largest office buildings.