joint baseUS military Joint Base Andrews, just outside of Washington, was on Thursday put on lockdown following reports of an active shooter at a medical centre.

Known as “America’s airfield”, Andrews is the home base of Air Force One, the airplane used by the US presidents. A “shelter in place” order was in effect at the base.

However later, FBI and Maryland State Police confirmed that the situation was a scheduled drill.

The incident was reportedly unfolding at the Malcolm Grow Medical Facility, the base authorities said. There were no reports of actual shots fired, however.

The shooter was barricaded on the third floor of the medical centre, according to a reporter for the military newspaper Stars and Stripes.

There appeared to be some confusion whether the situation was real or part of a scheduled exercise. Base officials said the call came during an exercise but the report was real.

“We are reacting to a report of a real-world active shooter,” a spokesperson for the base told WTTG TV.

“The call occurred during an exercise. Because the report came in as a real active shooter, we have to respond accordingly. We are treating as if it is and no further information at this time.”