Ward said security officers started directing people out of the building with guns drawn.
One person died at George Washington University Hospital of a single gunshot wound to the left temple, said Dr. Babak Sarani, director of trauma and acute care surgery. A police officer and two civilian women were in critical condition at Washington Hospital Center, said Janis Orlowski, the hospital's chief operating officer.
Orlowski said the police officer was in the operating room with gunshot wounds to the legs. The police chief said the officer was wounded when he engaged the shooter who later died.
One woman at the hospital had a gunshot wound to the shoulder. The other had gunshot wounds to the head and hand.
Adm. Jonathan Greenert, chief of naval operations, was at the base at the time the shooting began but was moved unharmed to a nearby military installation
Anxious relatives and friends of those who work at the complex waited to hear from loved ones.
Tech Sgt. David Reyes, who works at Andrews Air Force Base, said he was waiting to pick up his wife, Dina, who was under lockdown in a building next to where the shooting happened. She sent him a text message about being on lockdown.
"They are under lockdown because they just don't know," Reyes said. "They have to check every building in there, and they have to check every room and just, of course, a lot of rooms and a lot of buildings."
Naval Sea Systems Command is the largest of the Navy's five system commands and accounts for a quarter of the Navy's entire budget. Only security personnel were allowed to be armed on the grounds.
Mason, the program management analyst for the Navy, said there are multiple levels of security to reach his office. Everyone must show a building ID to get through a main gate, and at the building entrance, everyone must swipe a badge to pass through either a door or gate, depending on the entrance.