Numerous firefighters and paramedics have responded to Joint Base Myer-Henderson Hall in Arlington, Va. for a hazmat situation.

Firefighters were first dispatched to Henderson Hall, the headquarters of the U.S. Marine Corps, just after 4:30 p.m. for a hazardous materials call.

Pentagon sources tell CBN News an envelope with an unknown substance was opened and several people fell ill.

CBN News has confirmed 11 people became sick and were treated.

An evacuation of the building and the deployment of an emergency decontamination unit was called to the scene.

People were reportedly being treated for symptoms that included a nosebleed and a burning sensation. 

Thus far there is no official word as to the nature of what happened or the substance involved.

Police are closing off roads near the entrance to Henderson Hall, at the intersection of S. Orme Street and Southgate Road.