The U.S. Coast Guard opened fire on Thursday on a derelict Japanese fishing vessel washed out to sea by last year's devastating tsunami in a bid to sink it and eliminate a threat to navigation, a spokesman for the agency said.

The Coast Guard, which hopes to send the ship to the ocean floor, fired on the vessel with a 25mm machine gun, said Petty Officer First Class David Mosley, a spokesman for the Coast Guard.

At last report the vessel was on fire and listing in the sea, as the cutter crew took a break to evaluate progress of the operation, Mosley said.

Plans to sink the fuel-laden ship had earlier been put briefly on hold because a fishing vessel was nearby.

The captain of that vessel, the Bernice, had expressed an interest in salvaging the abandoned Japanese ship, but once on the scene the captain decided it was not safe to salvage or tow it, the Coast Guard said.

The ship's Japanese owner has also said it has no plans to salvage the vessel. The Ryou-Un Maru, nicknamed a ghost ship for its abandoned state, is among the 1.5 million tons of debris the Japanese government estimates was dragged out to sea by last year's tsunami, said Ben Sherman, a spokesman for the National Oceanic and Atmospheric Administration.

This boat, in this case, we know was at a particular pier, and before the tsunami it was there and after the tsunami it wasn't, Sherman said.

Experts from NOAA and other agencies determined that sinking the ship was the best way to manage the potentially dangerous fuel on board, Sherman said. They anticipate that it'll dissipate or evaporate very quickly, he said.

Although most of the tsunami debris expected to hit U.S. coastlines is predicted to arrive in 2013 or later, some items have already washed ashore. In Alaska, most of the marine debris identified as tsunami-related has been buoys and floats from oyster farms.

The Ryou-Un Maru, carrying up to 2,100 gallons of diesel fuel, was about 170 nautical miles southwest of the Alaskan town of Sitka and has been drifting toward busy navigational lanes used by cargo vessels plying the waters of the Great Circle route between North America and Asia, said U.S. Coast Guard Chief Petty Officer Kip Wadlow.

The Great Circle arcs from the U.S. West Coast to east Asia, passing through the Aleutian Islands.

The ship was initially spotted by Canadian officials in waters off the coast of British Columbia, Wadlow said. It drifted into U.S. waters on Saturday, and the U.S. Coast Guard began its close monitoring of the vessel.

The ship lacks lights, making it a dangerous obstacle at night, Wadlow said.

(Editing by Alex Dobuzinskis, Cynthia Johnston, Todd Eastham and Lisa Shumaker)