Joint Base Andrews in Maryland is under a state of alert with a facility wide lockdown in effect following reports of an active shooter.
The lockdown was imposed at 13:00 BST, according statements posted online by the base. As a result all staff and military personnel have been directed to shelter.
"The incident is ongoing at the Malcolm Grow Medical Facility. First responders are on-scene now. All personnel continue to shelter in place," authorities at Andrews have said.
FOX 5 DC has reported that a drill was due to take place at Andrews today (30 June) whether the reports of an active shooter the drill are connected is unclear.
The base, the home of the US Presidential jet Air Force One, contains emergency reaction forces for deployment in Washington DC.
The facility was previously known as Andrews Air Force Base before it merged with the Naval Air Facility in 2009.