Washington's main railway terminal, Union Station, was evacuated on Wednesday because of a bomb threat, a police officer told Reuters.

"We got a bomb threat," the officer, who did not give his name, said as he urged people to leave Union Station in downtown Washington near the U.S. Capitol Building.

Panicked people began running out of the station, which is a hub for railway, commuter train and subway service to the U.S. capital city, shortly after 5 p.m. EDT (2100 GMT), a Reuters witness said.

A bomb-sniffing dog walked among people standing outside the massive building.

Police cars, a fire truck, an ambulance and a police canine vehicle converged on the railway station.

(Reporting by Arshad Mohammed and Michelle Nichols; Editing by Eric Beech and Sandra Maler)