UPDATE 6:18 a.m.: All lanes of Key Bridge have reopened, AP reports.

A D.C. officer is in stable condition after he was struck by a vehicle while investigating an accident on the Francis Scott Key Bridge, police say.

Authorities say the initial crash occured around 10:50 p.m. Sunday. About an hour later, police say, the officer was directing traffic around the accident when he was hit from behind by another vehicle. Upon impact, he was thrown into the windshield of the vehicle. The striking vehicle remained on the scene.

Police say the officer sustained head injuries, but is alert and in stable condition at George Washington Hospital.

As of 4:06 a.m. Monday, the Key Bridge remains closed in both directions.

Authorities say the Metropolitan Police Department has requested that the driver of the striking vehicle undergo a sobriety test.