WASHINGTON (CBSDC/AP) — At least one gunman opened fire inside a building at the Washington Navy Yard on Monday morning, and officials said six people were killed and at least four were wounded, including a law enforcement officer.

Police were looking for two other potential gunmen wearing military-style uniforms, including one who had on a beret, chief Cathy Lanier said. One had a long gun and the other was also armed, she said. Lanier said she didn’t think the other gunmen were part of the military.

One of the three gunmen had died, though Lanier didn’t say how.

Authorities have identified the dead shooter as a Navy employee whose work status had been changed earlier this year, said a federal government official who spoke only on condition of anonymity because he wasn’t authorized to speak on the record. While that may suggest the motive was job related, authorities haven’t ruled out anything including terrorism, the official said.

Witnesses described a gunman opening fire from the fourth floor, aiming down on people in the first-floor cafeteria. Others said a gunman fired at them in a third-floor hallway. It wasn’t clear whether the witnesses on different floors were describing the same gunman.

As witnesses emerged from the building, a helicopter hovered over it, schools were on lockdown and airplanes at nearby Reagan National Airport were briefly grounded so they wouldn’t interfere with law enforcement helicopters. Less than 2 miles away, security was beefed up at the Capitol, but officials said there was no known threat there. President Barack Obama was getting frequent briefings on the shooting.

Two Navy officials confirmed at least six people had died in the rampage at started around 8:20 a.m. Monday at the Naval Sea Systems Command Headquarters building. About 3,000 people work at the Naval Sea Systems Command headquarters. The officials spoke on condition of anonymity because they were not authorized to discuss the situation publicly.

Lanier says one police officer was wounded in an exchange of gunfire with a shooter.

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 turned and started firing,” Brundidge said.

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

“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.’”

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. He said the gunman was aiming down at people in the building’s cafeteria on the first floor. Mason said he could hear the shots but could not see a gunman.

Shortly after the gunfire, Mason said someone on an overhead speaker 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.

“Everybody just panicked at first,” she said. “It was just people running, running, running.”

Ward said security officers started directing people out of the building with guns drawn.

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.

Among the wounded was a D.C. police officer, according to a law enforcement official who spoke on the condition of anonymity because the person was not authorized to discuss an ongoing investigation.

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

The 11th Street Bridge is closed in both directions due to heavy law enforcement presence. M Street is closed near New Jersey Avenue and 11th Street.

Bolling Air Force Base is closed and six D.C. schools are on lockdown. Amidon-Bowen Elementary School, Brent Elementary School, Eastern High School, Eliot-Hine Middle School, Jefferson Academy, Tyler Elementary School, and the Van Ness Administration Building are all locked down, school officials say.

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 says family members looking for information about their loved ones can call 202-433-6151 or 202-433-9713.

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Source: CBS