Police sources told The Washington Post that three shooters, including one in military fatigues, were involved in the incident.
Roughly 3,000 people who work inside the building have been directed to stay in place as authorities continue searching for the shooter, Navy officials said. Low-flying helicopters were spotted circling above the scene, dropping baskets to evacuate people from the complex.
The Washington Post reported that a D.C. police officer was among those injured. All were listed in critical condition, authorities told the newspaper.
Rick Mason, a program management analyst who is a civilian with the U.S. Navy, said a gunman was shooting from a fourth floor overlook in the hallway outside his office. Mason said the gunman was aiming down at people in the building's cafeteria on the first floor, adding that he could hear the shots but could not see a gunman.
Shortly after the gunfire, Mason said overhead speakers told workers to seek shelter and later to head for the gates at the complex.
Patricia Ward, a logistics management specialist, said she was in the cafeteria and heard shots. They sounded like "pop, pop, pop," she said. After a few seconds, there were more shots, she said.
"Everybody just panicked at first," she said. "It was just people running, running, running."
People who were inside the building said the gunman — described as a tall, African-American male — wordlessly sprayed fire from an AR-15 assault rifle.
“We saw him hold the rifle, and we saw him aim it in our direction,” a witness told FoxNews.com.
Another witness told WJLA: "We were looking, but he was down the hall far enough that we couldn't see a face. But we saw him hold the rifle and then we saw him raise it and aim in our direction."
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. It builds, buys and maintains the Navy's ships and submarines and their combat systems.
