LIVE: BBC news coverage of the shooting at the Washington Navy Yard
At least six people have been reported killed in a mass shooting at the Washington Navy Yard in the US capital.
At least four others including a police officer were injured, officials said.
Shots were reported at 08:20 local time (13:20 GMT), and dozens of armed police officers converged on a building at the naval installation.
A gunman was killed at the scene and police are searching for two other "potential" gunmen, Washington Police Chief Cathy Lanier said.
Officials are searching the area surrounding the Navy Yard in south-east Washington DC for two additional suspects in military-style uniform, Ms Lanier said.
"The big concern for us right now is that we potentially have two other shooters that we have not located," she said.
She described one as a white male in a tan short-sleeve military-style outfit and beret hat. He was last seen about 08:35 local time carrying a handgun.
A black male approximately 50 years of age and wearing olive kit was seen carrying a long gun and is also being sought.
'Severe' injuries
Gunman 'aimed at us'
Washington Mayor Vincent Gray said four people were wounded in the shooting. Ms Lanier said "multiple victims" were deceased. On Monday afternoon local media reported at least six people were killed.
The shooting occurred at a building on the campus that serves as the headquarters for the Naval Sea Systems Command yard.
At least three people suffering "severe" gunshot wounds were brought to Washington Hospital Center by helicopter, said chief medical officer Janis Orlowski.
A Washington DC Metropolitan Police officer suffered multiple gunshot wounds to his legs, a female civilian was shot in the head and hand, and another woman was being treated for a shoulder wound, she said.
All three were in critical condition but their chances for survival were "very good", Dr Orlowski said.
Continue reading the main storyEyewitness Patricia Ward reported hearing at least seven shots from inside a cafeteria on Monday morning.
"It just happened so fast… I just ran," she said.
Cmdr Tim Jirus was on the fourth floor of the building when he heard shots, he told the BBC.
"It sounded like a cap gun as opposed to a real gun," he said. "I feel very lucky to be alive. Someone standing there talking to me got shot. I didn't."
'Unimaginable violence'
Professor Gary Solis explains what the Washington Navy Yard does
The Washington DC Metropolitan Police Department has instructed family members to reunite at the car park of a nearby baseball stadium.
President Barack Obama has been briefed on the matter by senior aides and has directed federal agencies to co-ordinate their response and investigation efforts.
At the White House, Mr Obama said he mourned "yet another mass shooting" and sent his thoughts and prayers to the victims.
"These are men and women going to work and doing their job," he said. "They know the dangers of serving abroad, but today they face the unimaginable violence that they wouldn't have expected here at home."
As many as 3,000 people work at the command, which engineers, purchases, builds and maintains ships and submarines for the Navy.
The Washington Navy Yard is the US Navy's oldest shore installation, first opened in the early 19th Century, according to the Navy.
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