Joint Base Andrews outside Washington, D.C., went into lockdown Thursday morning after a preparedness drill was mistakenly reported as an active shooter situation.

ADVERTISEMENT

After about an hour and a half, officials lifted the lockdown for all parts of the base except the Malcolm Grow medical facility.

The FBI, Maryland State Police and Prince George's County police all said the incident was a drill, according to WUSA9 news.

#BREAKING: FBI and Maryland State Police confirm Joint Base Andrews situation to be a DRILL. — WUSA9 (@wusa9) June 30, 2016

#BREAKING: Prince George's County police and fire spokespersons say shooter incident at Joint Base Andrews is a CONFIRMED DRILL. — WUSA9 (@wusa9) June 30, 2016

The base, located nearby in suburban Maryland, tweeted shortly after 9 a.m. that all personnel should shelter in place as it worked to provide more information.

The base added that the incident was at a medical facility and first responders were on scene.

JBA is currently on lockdown due to a report of an active shooter. All personnel are directed to shelter in place. More info as it comes. — Joint Base Andrews (@JBA_NAFW) June 30, 2016

The incident is ongoing at the Malcolm Grow Medical Facility. First responders are on-scene now. All personnel continue to shelter in place — Joint Base Andrews (@JBA_NAFW) June 30, 2016

ADVERTISEMENT

The base said in a tweet that while there was an active shooter exercise, there were also "reports of a real-world active shooter situation," defending its move to shut down the base "due to the serious nature of this report."

Andrews is the home of Air Force One, the presidential aircraft. President Obama, Vice President Biden and foreign dignitaries routinely use the base to fly into and out of Washington.

Obama was at Andrews just 12 hours before reports of the shooter broke, when he returned to the nation’s capital after meeting with North American leaders in Ottawa, Canada.

Homeland Security Secretary Jeh Johnson, who was testifying before the Senate Judiciary Committee on Thursday morning, described the event as an "unfolding situation at Andrews Air Base," which he warned may force him to leave the hearing, though he ended up staying.

Vice President Biden's travel to Ohio was delayed by the incident at Andrews, according to NBC News, which reported that the vice president was not at the base.

Biden was scheduled to attend an event for Gov. Ted Strickland in Columbus before giving a speech in Cleveland on his cancer moonshot effort, followed by another Strickland event.

Last month, the base was placed on lockdown after a woman at the visitor's center claimed to have a bomb, though none was found.

—Jordan Fabian and Julian Hattem contributed to this breaking news report, which was updated at 10:45 a.m.