This post has been updated.

Joint Base Andrews is “all clear,” according to a tweet from the air force campus, which was placed on lockdown this morning after officials received a report of an active shooter.

As dozens of people evacuated the Malcolm Grow Medical Facility, Prince George’s County officials, who would normally assist during a security incident, said that “it was not assisting with any emergency response,” NBC4 reported.

Around 10:15 a.m., Mark Brady, spokesperson for the Prince George’s County Fire Department tweeted that he was learning that it “was an exercise.”

The base was placed on lockdown around 9 a.m. after a report of an active shooter on the Air Force campus. First responders reported to the Malcolm Grow Medical Facility, and everyone on site was directed to shelter in place.

The campus was scheduled to have an active shooter drill this morning, but officials said they received reports about a “real-world active shooter situation” during that time, according to the base.

Located in Prince George’s County, Md., the base is home to Air Force One.