Hazmat units respond to Pentagon 'hazardous materials' incident

Specialized hazardous materials teams from the Arlington County Fire Department (ACFD) joined Pentagon security forces Thursday to address a potential airborne threat at the US military headquarters.

"ACFD units ... are currently operating at the Pentagon in support of PFPA's (Pentagon Force Protection Agency) Hazmat Team during a hazardous materials incident," said the local fire department.

Pentagon spokesperson Sean Parnell told CNN that monitoring systems identified an air quality issue, prompting a "shelter-in-place order for the affected area."

CNN said multiple floors and corridors are under lockdown while personnel evacuate other sections of the complex.

Law enforcement officers inside the building reportedly donned full chemical protective gear and gas masks, sources told CNN.