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, D.C., police officer who has been hospitalized, and another law officer not affiliated with the city force, said Metropolitan Police Department spokesman Chris Kelly.
The incident occurred at 8:20 a.m. when several shots were fired inside the headquarters for Naval Sea Systems Command in southeast Washington, D.C. An "active shooter" remained inside the building, the Navy said.
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.
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, D.C., 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 has been 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.