“An active shooter was reported” at roughly 8:20 a.m. inside the headquarters building, according to the Navy.
A D.C. police officer and a base security officer were among the reported victims.
About 3,000 people, both civilian and military, work at the Naval Sea Systems Command Headquarters.
Navy Capt. Danny Rodriguez said he was in an adjoining Navy Yard building when the shooting started.
“Everybody rushed in,” to the building where he was, and security guards locked down the facility.
“It was pretty orderly,” he said.
Rodriguez said in a cellphone conversation that the lockdown was still in effect.
A White House official reported that President Barack Obama had been briefed on the situation.
“The president has been briefed several times about the unfolding situation at the Washington Navy Yard by Assistant to the President for Homeland Security and Counterterrorism Lisa Monaco and Deputy Chief of Staff Alyssa Mastromonaco,” the spokesman said.
“The president directed his team to stay in touch with our federal partners, including the Navy and FBI, as well as the local officials. We urge citizens to listen to the authorities and follow directions from the first responders on site.”