WASHINGTON (CNN) — A gunman dressed in all black fired shots Monday inside the U.S. Navy Yard, injuring at least 10 people, according to the Navy and a Washington police spokesman.
The U.S. Navy tweeted there are "several confirmed injuries with reports of fatalities."
The injured included a Washington police officer who has been hospitalized, and a base security guard officer, said Metropolitan Police Department spokeswoman Saray Leon.
The incident occurred at 8:20 a.m. when several shots were fired inside the headquarters for Naval Sea Systems Command in southeast Washington. An "active shooter" remained inside the building, the Navy said.
Helicopters hovered overhead as police with riot and SWAT team gear swarmed the scene.
Police spokesman Chris Kelly described the suspect as an adult male, about 6 feet tall with a bald head and medium complexion, dressed in a black top and black jeans.
Two witnesses told CNN affiliate WJLA that they heard a fire alarm go off in the building where they worked, then saw a man with a rifle down the hallway as they exited the building.
"He aimed the gun and fired our way," a man who identified himself as Todd Brundidge told WJLA, adding, "I couldn't believe it."
People frantically tried to run out of the building, Brundidge said.
"Everyone was going down the stairs. They were pushing. They were shoving. People were falling down," he told WJLA. "As we came outside, people were climbing the wall trying to get over the wall to get out of the spaces. It was just crazy."
Emergency personnel, the FBI, U.S. Capitol Police and local D.C. police responded to the shooting, shutting down traffic in the area on the District's south side along the Anacostia River. Some people are being evacuated, and others are sheltering in place.
At least six schools were on lockdown as a precaution, the Washington public schools said in a Twitter post.
Air traffic to Reagan National Airport in northern Virginia, the closest airport to downtown Washington, was suspended but later resumed, the Federal Aviation Administration said.
A White House statement said President Barack Obama was briefed on the situation.
The headquarters -- the workplace for about 3,000 people -- is the largest of the Navy's five system commands. It has a fiscal year budget of nearly $30 billion.
"With a force of 60,000 civilian, military and contract support personnel, NAVSEA engineers, builds, buys and maintains the Navy's ships and submarines and their combat systems," the Navy said.
The Washington Navy Yard -- the Navy's oldest land establishment -- was created in 1799 following an act of Congress, according to the Naval History and Heritage Command. Originally envisioned as a shipbuilding and fitting facility on the Anacostia River, it serviced some of the Navy's most famous early vessels, including the USS Constitution.
Burned during the War of 1812, the Navy Yard was transformed into a center for ordnance and technological development. The facility was the world's largest ordnance plant during World War II, but its military role steadily diminished during the Cold War era.
Today, the Navy Yard includes the headquarters of Naval District Washington and is home to a naval museum. The area around the facility has been marked in recent years by significant commercial and residential revitalization.
-- CNN's Brian Todd, Alan Silverleib, Joe Sterling, Dan Merica, Barbara Starr, Paul Courson and Evan Perez contributed to this report.