Police in Washington DC have confirmed 12 dead and several others critically wounded after being shot today in a building at the Washington Navy Yard in DC.

Chief Cathy Lanier says police are looking for a white man and a black man wearing military-style clothing, according to reports in the American media.

The reports said witnesses described a scene of fear and chaos as employees flee buildings or lock selves in offices.

Authorities said one of the dead was a gunman – identified only as a Navy employee whose work status had been changed earlier this year. He had been armed with an assault rifle, a handgun and possibly a rifle, officials said.

“We potentially have two other shooters that we have not located at this point,” said Metropolitan DC Police Chief Cathy Lanier. “We have information to believe neither of these folks are military personnel. These are people we really believe were involved in some way. … We are still doing an extensive search,” she added.

Rick Mason, a civilian program management analyst with the Navy, said one of the gunmen was shooting from a fourth-floor overlook in the hallway outside his office — aiming at people in the cafeteria on the first floor.

Navy employee Todd Brundivge said the shooter who suddenly confronted him and his fleeing coworkers in a hallway was chillingly silent.

“No words. He raised the gun and started firing. He said nothing,” Brundivge told NBC.

Navy Cmdr. Tim Jirus told The New York Post that he fled the building and was standing in an alley with another man when they heard two shots around 8:45 a.m.

He said he turned to look, and when he turned back again, the man next to him “was shot in the head.

“It’s crazy. You come to work on a Monday, and the next thing you know, there are people inside your building shooting the people you work with,’’ he said.

Those shot in the mayhem — about 2.5 miles from White House — included a DC Metro police officer who took two bullets to the leg, and a security guard at the base.

One victim — described only as a man in his 60s — died at George Washington Hospital, authorities said.

Washington Hospital Center said it received three of the wounded, including the male DC officer and two women — one of whom was shot in the head. All were expected to survive, said Chief Medical Officer Janis Orlowski.

While they came in “alert, talking, they do have severe injuries,” she said.

“They haven’t been able to give us any information about what happened to them. Obviously, they’re in pain and distress.”

As for the weapon used on them, “it had to be a semi-automatic,” Orlowski said, “because they’re talking about gunshots they heard in rapid succession.”

The US Navy said shots were first fired around 8:15 a.m. at the Naval Sea Systems Command Headquarters building, where about 3,000 people work.

“The fire alarm went off first. I was on the phone, and somebody came up to my desk and said, ‘Hey, that’s not a fire alarm! Somebody’s been shot in the building!’ ” Brundivge told CNN.

“So we went around trying to get people out of the building, and when we went to the back door, we noticed [the shooter] was down the hall, and he stepped around the corner, and as he came around the corner, he aimed his gun at us, and he fired two or three shots.

“And we ran down the stairs to get out of the building. Eveyrbody was going down the stairs, people were pushing, people were shoving. When we came outside, people were climbing the wall trying to get over the wall,” Brundivge said.

“After we left, there were still shots. … I couldn’t believe it. You go to work, you never believe this is gonna happen to you.”

A grim-faced President Obama condemned “the cowardly act.

“We do know some people have been shot and some people have been killed,” he told reporters. “We are confronting yet another mass shooting, and it today, it happened on a military installation in our nation’s capital.”

The White House issued a statement on the shooting saying counterterrorism officials were investigating:

“The president has been briefed several times about the unfolding situation at the Washington Navy Yard by Assistant to the President for Homeland Security and Counterterrorism Lisa Monaco and Deputy Chief of Staff Alyssa Mastromanaco. The president directed his team to stay in touch with our federal partners, including the Navy and FBI, as well as the local officials. We urge citizens to listen to the authorities and follow directions from the first responders on site.”

A police spokesman said one officer was shot near the room where a gunman has barricaded himself.

Flights were being held at nearby Reagan National Airport as helicopters buzzed over the facility and cops cordoned off nearby streets.

A “shelter in place” order has been issued for Navy Yard personnel, authorities said.

The Washington Navy Yard said on its website that it’s the Navy’s oldest shore establishment.

The yard is home to the chief of Naval Operations and is also headquarters for the Naval Historical Center and numerous naval commands.

•Photo: People exit a Navy Yard building with their hands above their heads.