Joint Base Andrews on lockdown amid reports of shooter

US Joint Base Andrews outside Washington, the home base of the presidential plane Air Force One, was placed on lockdown Thursday amid reports of a shooter, the military facility said on Twitter.

"The incident is ongoing at the Malcolm Grow Medical Facility. First responders are on scene now. All personnel continue to shelter in place," the base said.

"The base was scheduled to conduct an active shooter exercise, however, reports of a real-world active shooter situation were reported."

On Capitol Hill, Homeland Security Secretary Jeh Johnson told lawmakers there was an "unfolding situation" at the base, adding he might need to take a break in his testimony to address the situation.

The situation delayed the travel of Vice President Joe Biden, who was due to head to Ohio for a campaign event, according to his office.

Joint Base Andrews, located in Maryland, is home to thousands of military personnel and their families. US President Barack Obama regularly plays golf on the base.