A standoff was underway late Friday between police and a man with a gun on a boat in the Potomac River, authorities said.

The incident, which had gone on for hours, was continuing just before midnight Friday off the Belle Haven Marina, which is in the Alexandria section of Fairfax County, south of the Woodrow Wilson Bridge.

U.S. Park Police Sgt Paul Brooks said the matter began about 6 p.m. when shots were reportedly fired in the area of the marina. A man then jumped into a dinghy, took it out to a larger boat, and jumped aboard.

The marina was evacuated, and police were trying to contact the man , Brooks said.

He said there were no reports of injury, and it was not known why the shots were fired.