A US air base, that is home to the Presidential plane Air Force One, was on lockdown over reports of an active shooter on site.

Messages on the Twitter and Facebook pages of Joint Base Andrews in Maryland say that the situation is now "All Clear" with the exception of the Malcolm Grow Medical Facility on site.

"All Clear" for the base with the exception of Malcolm Grow medical facility

— Joint Base Andrews (@JBA_NAFW) June 30, 2016

Their Twitter account earlier confirmed that a shooter was "active" and instructed all personnel at the base in the Washington DC suburbs to find shelter and stay in place.

The statement said: "There were reports of an active shooter incident on base at Malcolm Grow medical facility at approximately 9am (local time) today, June 30, 2016.

"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.

"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."