(AP) -- The military base outside Washington where the presidential plane Air Force One is stationed was temporarily locked down Thursday after an "active shooter" report that turned out to be a false alarm.

The report stemmed from someone who made a distress call after seeing security forces doing a routine inspection. The confusion was heightened by a planned active-shooter drill at Joint Base Andrews that had not yet begun. Officials said in a Facebook post Thursday that there was no shooter and no threat to the base or workers there.

The base about 20 miles from Washington was placed on lockdown about 9 a.m. About an hour and a half later, the military post tweeted that the lockdown had been lifted, except for the medical building where the active shooter was reported. In a later statement, the base confirmed there was no gunman and no threat to public safety.

"Fortunately, this was not a life-threatening situation," Col. Brad Hoagland, 11th Wing and base commander, said in the post. "We take all threats seriously and reacted to ensure the security of those on the base."

Joint Base Andrews is home to the presidential air fleet, and the president, vice president and other senior government officials fly in and out of the base. Vice President Joe Biden was scheduled to leave from Andrews on Thursday morning, but his trip was delayed by the lockdown. Biden was due in Columbus, Ohio, for a midday campaign event for former Gov. Ted Strickland, who is running for Senate.

President Barack Obama was last at the base Wednesday night when he returned from a trip to Ottawa, Canada.

Defense Secretary Ash Carter said the situation was handled relatively well, despite the apparent communication problem that led to the false report.

"I think we need to pay attention to how to minimize the chances of false alarms like that," Carter said. "At the same time, I think it's important to have a reasonable level of awareness of the possibility of this kind of event and what to do, and I thought the response was strong and solid."

Emergency vehicles in the area of the base had on lights Thursday, but no sirens. At least three people in camouflage and helmets could be seen walking working dogs around the three-story medical building. About 10:15 a.m., a few people could be seen walking out of the building, including a person being moved in a wheelchair.

Chris Grollneck, an active-shooter-prevention consultant who has worked on training at Army and Air Force bases, said the response to the report at Andrews was well-orchestrated and shows how much the military's training for active-shooter situations has improved. He also said the person who reported the shooter should be praised for taking the "see something, say something" message seriously.

"There was no catastrophic failure," Grollneck said. "Everybody took a pause, everybody evaluated what was going on and they started bouncing information off one another and realized there was no shooter."

Rodney Smith, the patient advocate at the Andrews medical facility, said he knew about the scheduled active-shooter exercise but then got reports of a real shooter and was told to stay in place.

"First it was an active-shooter exercise. Then it came back 'real world,'" Smith said by phone during the lockdown Thursday morning.

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Nuckols reported from Washington. Associated Press writers Sarah Brumfield, Robert Burns and Eric Tucker in Washington.

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This story has been corrected to show that Ted Strickland is a former, not current, governor of Ohio.