09/16/2013 09:11 EDT | Updated 11/16/2013 05:12 EST

U.S. navy yard shooting in Washington injures 4

At least four people, including a police officer, were shot today inside a military building at the Washington Navy Yard in the U.S. capital, according to Reuters.

A police spokesman told the news agency that an officer is among those hit by gunfire. Their conditions aren't immediately known.

Police and emergency crews were massing outside the Naval Sea Systems Command Headquarters building, where a gunman was believed to be holed up.

The Washington Navy Yard says on its website that it's the U.S. navy's oldest shore establishment. About 3,000 people work in the naval command building.

Workers have been told to stay where they are, and streets in the area have been closed.

Naval Sea Systems Command builds, buys and maintains the navy's ships and submarines and their combat systems.