UPDATE: Sadly, NBC Washington reports that the number of fatalities has increased to 13, including the gunman. He has been identified as 34-year-old Aaron Alexis of Fort Worth, Texas. Authorities are still searching for a possible second suspect. The Washington Post says the Navy Yard will be closed tomorrow.

NBC Washington says that the number of casualties has increased to seven. The Washington Post says that the total is up to nine, including one of the shooters.

NBC News is reporting that a gunman is dead:

The Washington Post reports that four people have been killed. Authorities are also reporting that there are two shooters:

Law enforcement officials in D.C. report that there is an active shooter situation going on at the Navy Yard. NBC Washington says that ten people have been shot, including two law enforcement officers. According to a Metro Police Department spokesman, authorities received word of the shootingaround 8:25 a.m. this morning. NBC Washington also reports that a combination of MPD officers, FBI agents and SWAT team have responded to the situation. 

According to the Navy, shots were fired inside of the Naval Sea Systems Command headquarters just after 8 a.m. this morning:

We will update with more information as it becomes available.

[via DCist and NBC Washington]