Washington: Homeland Security Secretary Jeh Johnson said Thursday there was an “unfolding situation” at Joint Base Andrews in Washington’s Maryland suburbs but provided no further details.

The base instructed all personnel at the base to continue to shelter in place and stay inside.

It was not immediately clear if any shots were fired or if anyone was wounded.

A tweet from the base said the incident was ongoing at the Malcolm Grow Medical Facility. The base tweeted earlier Thursday it was on lockdown due to a report of an active shooter.

Johnson was testifying before the Senate Judiciary Committee. He said he might have to take a break from the hearing as the situation at Andrews develops.

Joint Base Andrews is located about 20 miles outside of downtown Washington, D.C. and is home to Air Force One.

Rodney Smith, the patient advocate at the Andrews medical facility, said an active-shooter exercise was scheduled for Thursday morning, and then he was told it was a “real-world” situation. He said he was on lockdown and didn’t have any more information.

“First it was an active-shooter exercise. Then it came back ‘real world,’” Smith said by phone Thursday morning.

Smith said the situation was unfolding at the newer of two buildings at the Malcolm Grow Medical Facility. He was in the older building.