UPDATE 3:29 PM EST: The US Navy say the situation was a drill.
Police are responding to reports of an active shooter at the Walter Reed National Military Medical Center in Bethesda. Police have not confirmed the situation but people in and around the facility have received alerts warning them to shelter in place until further notice.
Congressman Dutch Ruppersberger tweeted that he is at the hospital and has locked himself with a large group of people in a conference room.