Updated 10:39 a.m. ET.
Joint Base Andrews on Thursday morning lifted a lockdown after concluding reports of an active shooter were false.
The shelter-in-place order was issued around 9 a.m. after reports of an active-shooter at the Malcolm Grow medical facility on the military installation outside Washington, D.C. It was lifted around 10:35 a.m. for all areas except the facility after law enforcement officials deteremined the reports were unfounded.
"All Clear," the base posted on its Twitter and Facebook pages. "The lock down on base has been lifted."
The base had been holding an active-shooter training exercise at the time of the reports.
"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," it posted in a previous message. "First responders are currently on scene to secure the location.
"Due to the serious nature of this report, the base is reacting to ensure the safety of all personnel," it added. "More information will be released as it becomes available."
CNN reported the drill may have involved an accidental discharge of a firearm.
Multiple law enforcement agencies responded to the incident, including those from the base, Prince George's County and U.S. Park Police.
The installation located about 10 miles outside Washington, D.C., in Prince George's County, Maryland, is home to several thousand service members and their families. It also houses the two VC-25 aircraft known as Air Force One when the president is aboard.
Joint Base Andrews falls under the command of the Air Force's 11th Wing in the Air Force District of Washington. It was formed in 2009 after the merging of Andrews Air Force Base and the Naval Air Facility Washington.
The base most recently went on lockdown in May after a woman claimed to be wearing a bomb. That incident was determined to be a false alarm.
--Brendan McGarry can be reached at brendan.mcgarry@military.com. Follow him on Twitter at @Brendan_McGarry.
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