Washington Navy Yard shooting leaves 13 dead, including gunman Aaron Alexis

A SHOOTING rampage in the heart of a US Navy complex in Washington has left 13 people dead.

One shooter  identified as Aaron Alexis, 34, from Fort Worth, Texas, was killed after opening fire on police, but police were looking for one other possible gunman wearing a military-style uniform.

President Barack Obama said he was mouing "yet another mass shooting'' and called it a "cowardly act.''

Officials said at least three people were critically wounded in the rampage at the Washington Navy Yard, including a law enforcement officer. Hospital officials said all three were expected to recover.

It is believed the shooter's weapon was an AR-15, the same gun used in the Sandy Hook elementary school and Aurora cinema massacres.

Police had been looking into the possibility of an additional two shooters but at a 4pm press conference (6am AEST) ruled out one of those suspects as having any involvement.

The shooting led to tightened security at the Capitol and White House nearby, including shutting down the Senate while a possible remaining shooter was sought.

FBI photo of Aaron Alexis, the man identified as the US Navy Yard shooter. Picture: FBI

Washington DC Police Chief Cathy Lanier announced the death toll and said people were being told to stay in their homes and out of the area. Lanier said there was no indication of a possible motive. The fatalities includes the dead gunman.

Witnesses described a gunman opening fire from a fourth-floor overlook, aiming down on people in the first-floor cafeteria. Others said a gunman fired at them in a third-floor hallway.

Todd Brundidge, an executive assistant with Navy Sea Systems Command, said he and other co-workers encountered a gunman in a long hallway of their building on the third floor. The gunman was wearing all blue, he said.

"He just tued and started firing," Mr Brundidge said.

Navy officer Tim Jirus told reporters a co-worker was shot in the head just a metre away from him.

While struggling to understand what was going on, a man from the base's maintenance department spoke to Mr Jirus.

A shooting victim is taken off a helicopter and wheeled into hospital for treatment. Picture: NBC

"He walked up and told me he heard there was a shooter in our building. We were just standing here maybe three feet away having a conversation and we heard two more gunshots and he went down. That's when I ran," Mr Jirus said.

"I'm fairly certain he was dead because he was shot in the head.''

Alexis was using the ID of a man who used to work at the Navy Yard, NBC News reported. The news outlet said he was a civilian contractor who was identified through his fingerprints.

Police arrested the man whose ID was used but are yet to determine if he is an innocent victim or if he was connected to the shooter.

Alexis was a former reservist who had won the National Defence Service Medal and Global War on Terrorism Service Medal.

The Washington Post said Alexis grew up in Brooklyn with his mother, Sarah, and father, Anthony Alexis, according to his aunt Helen Weeks.

A screen grab of NBC Washington's coverage of a shooting at the Washington Navy Yard.

“We haven’t seen him for years,” Ms Weeks told the paper in a telephone interview. “I know he was in the military. He served abroad. I think he was doing some kind of computer work.”

The paper reported that Alexis spent nearly four years in the Navy as a full-time reservist from May 2007 until he was discharged in January 2011. The reason for his discharge was not immediately known.

DC Police Chief Cathy Lanier said police response had been outstanding and hailed those first responders as "heroes."

"The action of the police officers helped reduce the number of dead," she said.

Ms Lanier said that police were still looking at the prospect that their may have been one additional shooter.  He is described as African American, aged between 40-50, with gray sidebus and dressed in a military style uniform.  Police had ruled out another Caucasian man, around the same age, who was also dressed in a naval-type uniform.

FOLLOW LIVE COVERAGE OF THE SHOOTING HERE:

A Twitter picture from the Washington Navy Yard area.

Ms Lanier said a call came in at 8:15am about a shooter at the Navy yard and police were on the scene within seven minutes.  Other reports suggest that the initial shooter, who has since been killed, was carrying a military-style AR15 assault rifle, a shotgun and a handgun.

As emergency vehicles and law enforcement officers flooded streets around the complex, a helicopter hovered overhead, nearby schools were locked down and airplanes at nearby Reagan National Airport were briefly grounded so they would not interfere with law-enforcement choppers.

A helicopter lifts a person off the roof as police respond to the report of a shooting at the Navy Yard in Washington.

Dr Janis Orlowski from MedStar Washington Hospital Centre said three shooting victims, including a police officer, had been treated at the hospital and were all in a stable condition.

The police officer was shot in the legs and is currently in surgery.  A second woman had been shot in the shoulder and also had surgery, while a third woman was shot in the head and the hand but did not have surgery as the bullet to her head didn't not penetrate the bone.

"I have to say I may see shootings every day ... but there is something wrong when we have these multiple shootings," Dr Orlowski said.  "We have to work together ... I would like you all to help put my trauma centre out of business."

US President Barack Obama was getting frequent briefings on the shooting.  In a press conference he said he was in mouing for what he called "yet another mass shooting" in the United States that he says took the life of American patriots.

"We are confronting yet another mass shooting and today it happened on a military installation in our nation's capital," he said. The victims "are men and women who were going to work, doing their job, protecting all of us. They are patriots. They did not expect to be attacked at home while in their offices."

Mr Obama promised to make sure, quote, "whoever carried out this cowardly act is held responsible."

A U.S. Park Police helicopter removes a man in a basket from the Washington Navy Yard.

About 3000 people work at the Naval Sea Systems Command headquarters, which builds, buys and maintains the Navy's ships and submarines and combat systems.

'I saw co-worker shot in head'

Navy officer Tim Jirus told reporters a co-worker was shot in the head just a metre away from him.

Mr Jirus told CNN he had evacuated workers in his department after hearing what sounded like "muffled shots'' from a different part of the base.

"It sounded like a cap gun going off. A small calibre, if anything. Then about a minute or two after that, somebody was running through the hallway saying 'Hey, everybody, get out of the building,''' Mr Jirus said.

"I wanted to get everybody out of the building. We walked out."

Police tactical units leave after responding to a shooting at the Navy Yard in Washington, DC.

While struggling to understand what was going on, a man from the base's maintenance department spoke to Mr Jirus.

"He walked up and told me he heard there was a shooter in our building. We were just standing here maybe three feet away having a conversation and we heard two more gunshots and he went down. That's when I ran," Mr Jirus said.

"I'm fairly certain he was dead because he was shot in the head," he added.

"It's traumatic. I don't feel lucky he got hit instead of me but I feel lucky to be here.''

Todd Brundidge, an executive assistant with Navy Sea Systems Command, said he and other co-workers encountered a gunman in a long hallway of their building on the third floor. The gunman was wearing all blue, he said.

"He just tued and started firing," Mr Brundidge said.

An unidentified woman is reunited at the family gathering site outside parking lot B of Nationals Park, which has been set as a gathering point for families of the Navy Yard shootings in Washington DC.

Terrie Durham, an executive assistant with the same agency, said she also saw the gunman firing toward her and Mr Brundidge.

"He aimed high and missed," she said. "He said nothing. As soon as I realized he was shooting, we just said, 'Get out of the building.'"

Patricia Ward, a Navy logistics management specialist, said that she was at an ATM machine in the first floor atrium of Building 197, where the Naval Sea Systems Command is located, when she heard loud, short explosions coming from a few floors above the open lobby.

She and her two companions, who were on their way to breakfast, exchanged glances.

One of Ward's friends started to ask: "Was that a gunshot?" But she was interrupted by the sounds of "BAM BAM BAM BAM BAM," Ward said.

"We knew it then," Ward said. "We just started running."

Two DC Metro Police officers put their gear uonas they respond to a reported shooting at an entrance to the Washington Navy Yard.

Washington Redskins wide receiver Josh Morgan was doing a press conference about his side's lost on Sunday to the Green Bay Packers when he heard about the shooting at the the Navy Yards where his mother works.

Despite putting in 30 calls to his mum he heard nothing until his cousin tweeted him to tell him she was fine.  It is not the first time that the family has been at the centre of danger - his mother was working at the Pentagon during 9/11 and Morgan was a student at Virginia Tech during the 2007 massacre that killed 32 people.

Rick Mason, a program management analyst who is a civilian with the US Navy, said a gunman was shooting from a fourth floor overlook in the hallway outside his office. He said the gunman was aiming down at people in the building's cafeteria on the first floor. Mr Mason said he could hear the shots but could not see a gunman.

Shortly after the gunfire, Mr Mason said someone on an overhead speaker told workers to seek shelter and later to head for the gates at the complex.

Police and federal agents from multiple law enforcement agencies responded. Ambulances were parked outside, streets in the area were closed and departures from Reagan National Airport were temporarily halted for security reasons.

A US Park Police helicopter hovered over the building and appeared to drop a basket with a person onto the roof.

US President Barack Obama condemned the "cowardly" shooting at the Washington Navy Yard, and vowed a "seamless" operation to administer justice to those responsible.

District of Columbia schools officials said six schools and one administrative building in the vicinity of the Navy Yard were placed on lockdown. The action was taken out an abundance of caution, schools spokeswoman Melissa Salmanowitz said.

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.

The Navy Yard is part of a fast-growing neighbourhood on the banks of the Anacostia River in southeast Washington, just blocks from Nationals Park and about 2.5 kilometres southeast of the US Capitol.

Police respond to the report of a shooting at the Navy Yard in Washington, DC.

People hold their hands to their heads as they are escorted out of the building where a deadly shooting rampage occurred at the Washington Navy Yard. (AP Photo/Jacquelyn Martin)