Some 11 people reported feeling sick and several Marines received medical treatment after an envelope containing an "unknown substance" was opened around 3:30p.m. in an unidentified building on the Marine Corps side of Joint Base Myer-Henderson Hall in Virginia Tuesday.

Little information is available yet on what military and emergency response officials are calling a "HAZMAT" incident aboard the base, which abuts Arlington Cemetery.

In a statement, Marine Corps spokesman Maj. Brian Block said personnel in the building where the envelope was received evacuated immediately.

"Base officials and are coordinating with local HAZMAT teams and FBI," he said. "Several Marines are receiving medical care as a result of this incident. No additional details are available at this time as the investigation is ongoing."

UPDATE: Marines Released from Hospital after HAZMAT Incident at Joint Base Myer

A release sent late Tuesday evening by Joint Base Myer-Henderson Hall said Naval Criminal Investigative Service is also participating in the investigation.

The building, officials said, has been screened and cleared.

In a series of Tweets, the Arlington County Fire Department, which responded to the scene, said that three people were transported for further examination following their initial report of symptoms; all are in stable condition.

"Command is scaling back incident starting to put some units in service," the fire department said in a Tweet. "Investigation ongoing."

-- Hope Hodge Seck can be reached at hope.seck@military.com. Follow her on Twitter at @HopeSeck.