*A gunman wanted in connection with a Monday morning shooting at the Washington, D.C. Navy Yard that left four people dead and six others wounded has been killed, Washington’s NBC affiliate is reporting. According to DC’s police chief Kathy Lanier, potentially two more suspects – one white male last seen in the building with a handgun around 8:35 a.m., one African American male in his 50s carrying some sort of long gun, are still at large.

Among the dead, a man in his 60s shot in the temple.

A large search, including from helicopters, continues. “It’s a large piece of land with many buildings,” Assistant D.C. Police Chief Peter Newsham told News4. “It’s going to take a while to determine that it is safe.”

Tactical teams have entered at least two buildings on the Navy Base to search for the shooter, and News4’s Mark Segraves reported that three helicopters were seen tightly circling part of the base.

Earlier Monday morning, the gunman walked into Building #197 at the Naval Sea Systems Command Headquarters, 1336 Isaac Hull Ave. in the Southeast section of the District. He shot a security guard in the head, killing him, sources confirmed to News4’s Jackie Bensen.

The gunman then walked through the building, and seemed to target victims, Bensen reported. Some reports indicate he was armed with an AR-15, a military-style assault weapon.

D.C.’s Metropolitan Police Department and several other law enforcement agencies responded, Bensen said. During that response, a MPD officer was shot in the leg.

The gunman was then shot by a FBI hostage response team, Bensem said.

Washington Hospital Center said the MPD officer was among three victims that had been transported to that hospital. The officer was shot in the legs; one other victim was shot in the shoulder and one was shot in the head and hand.

All are alert and speaking at this time, and there is a “very good chance they will survive,” said Dr. Janis Orlowski, chief medical officer at the hospital.

However, the hospital has been prepared to expect more victims.

One victim was reported to be on the roof of a building, reported News4’s Tony Tull. A U.S. Park Police helicopter hovering above the scene around 9:50 a.m. lowered a basket to a building and lifted what appeared to be a shooting victim from the roof. The helicopter came back to the scene just after 10 a.m. to retrieve another victim.

But other details were sketchy from the scene. The shots continued to ring out through the morning, including a volley that Tull reported at about 9:20 a.m. and another volley that News4’s Mark Segraves heard at about 11 a.m.

Federal and local emergency personnel converged on the scene, “and a shelter in place order has been issued for Navy Yard personnel,” the Navy said. Among the responders was a federal SWAT unit.

President Barack Obama is getting frequent briefings about the deadly shooting from senior aides. The White House says Obama directed his team to stay in touch with the Navy, FBI and local officials as the events unfold.

D.C. Public Schools put six schools and one administrative building on lockdown, meaning no visitors or staff may enter or leave the building and recess for students is inside. These schools are affected:

Amidon-Bowen Elementary School
Brent Elementary School
Eastern High School
Eliot-Hine Middle School
Jefferson Academy
Tyler Elementary School
Van Ness Administrative Building
The following charter schools are also on lockdown:

Eagle Academy PCS – New Jersey Ave.
Friendship PCS Chamberlain Elementary and Middle.
Cesar Chavez PCS for Public Policy – Capitol Hill
Richard Wright PCS for Journalism and Media Arts
Somerset Prep DC PCS

The 11th Street Bridge and roads in the area are closed. Metro has also reopened New Jersey Avenue entrance at the Navy Yard station.

The Navy Yard is located in southeast Washington on the Anacostia River. The Navy says 3,000 people work inside the building, including command staff, headquarters directorates and field activities. They coordinate the Naval Sea Systems Command, or NAVSEA, the largest of the Navy’s five system commands.