The Pentagon confirmed an active shooter at Joint Base Andrews on Thursday, as the base directed its persoel to shelter in place.
A drill scheduled for Thursday moing had been cancelled and the base was calling the situation a "real world threat," according to Dylan Kuckolls, a senior airman and public information officer at JBA.
Homeland Security Secretary Jeh Johnson called the incident an "unfolding situation."
The FBI was actively monitoring the situation.
"There were reports of an active shooter incident on base at Malcolm Grow medical facility at approximately 9 a.m. today, June 30, 2016," the base reported on its Facebook page. "Persoel on base have been directed to shelter in place.
"The base was scheduled to conduct an active shooter exercise, however, reports of a real-world active shooter situation were reported at Malcolm Grow medical facility. First responders are currently on scene to secure the location."
JBA is currently on lockdown due to a report of an active shooter. All persoel are directed to shelter in place. More info as it comes.
— Joint Base Andrews (@JBA_NAFW) June 30, 2016
Rodney Smith, a patient advocate at the military post's medical facility, said the situation was unfolding at the newer of two buildings at the Malcolm Grow Medical Facility on the base. He was in the older building.
JBA is located in Prince George's County, Maryland. The base is located about 15 miles from the White House and is where Air Force One is parked.
Fox News' Lucas Tomlinson and The Associated Press contributed to this report.