One gunman died in the shooting, and police were last night seeking another possible shooter.
The Navy Yard was placed on lockdown after shots were fired inside a building on the base, the US Navy said. A Metro police officer and naval base officer were among those injured in the shooting.
The gunman was identified as Aaron Alexis, of Fort Worth, Texas a 34-year-old civilian contractor for the Navy.
Washington mayor Vincent Gray said he was shot during an exchange with the Metro police officer. “As far as we know, it’s an isolated incident. We have no known motive at this stage,” he said.
The mayor said there was “no reason at this stage” to believe it was terrorism, but would not rule it out.
DC police chief Cathy Lanier said authorities were seeking a potential second suspect, described as a black male, approximately 40 to 50 years old, 5ft 10in, 180 pounds, medium complexion with grey sideburns, wearing an olive military-style uniform and carrying “a long gun”.
Before a scheduled economic speech at the White House, President Barack Obama deplored “yet another mass shooting” — this one targeting military and civilian personnel.
“These are men and women who were going to work, doing their job, protecting all of us,” Obama said. “They’re patriots, and they know the dangers of serving abroad. But today they faced the unimaginable: Violence that they wouldn’t have expected here at home.
“We will do everything in our power to make sure that whoever carried out this cowardly act is held responsible. I want the investigation to be seamless.”
Janis Orlowski, chief medical officer at Washington Hospital, said one Metropolitan police officer and two civilians are being treated there. All three arrived in critical condition, but are expected to make a full recovery.
One was shot in the legs, another in the shoulder. Those victims were in surgery, Orlowski said. A woman who was shot in the head and hand would not need surgery because the bullet did not penetrate her skull.
The Navy said shots were fired at the Naval Sea Systems Command Headquarters building on the base at 8.20am (1.20pm Irish time) and a “shelter in place” order was issued for Navy Yard personnel.
Rick Mason told Yahoo! News he was on the fourth floor when he saw someone with a shotgun aiming down into the atrium. The gunman, Mason said, was targeting people who walked into the cafeteria.
Other employees described a chaotic scene.
“We heard two shots and started wondering if that was the sound of someone dropping something or if they were really shots,” said Omar Grant, a civilian employee at the Navy Yard who was on the first floor of the atrium.
“We heard three more shots, and that’s when people started running out of the building and getting the hell out of there.”
Grant then led a blind colleague to safety.
Approximately 3,000 people work in the building, the Navy said, although it’s unclear how many people were inside at the time of the shooting.
The Senate was locked down “in light of the uncertainty surrounding the shooting at the Navy Yard... and particularly the possibility of suspects remaining at large”, the Senate said in an alert to staffers.
“You may move about the building; however, for the next two hours you may not leave nor can anyone enter the building.”
A heavy SWAT and police presence could be seen around the Navy Yard. Outside the base, employees sat huddled, crying and holding each other.
The Navy Yard is home to the chief of naval operations and headquarters for the Naval Historical Centre and numerous naval commands.