OVER THE GULF OF ALASKA - A U.S. Coast Guard cutter poured cannon fire into a Japanese ghost ship that had been drifting since last year's tsunami, sinking the vessel in the Gulf of Alaska and eliminating the hazard it posed to shipping and the coastline.

The cutter's guns tore holes in the 164-foot Ryou-Un Maru on Thursday, ending the abandoned vessel's long, lonely journey across the Pacific. As the crew pummeled the ship, it burst into flames and began taking on water, officials said.

A huge column of smoke could be seen over the gulf as a Coast Guard C-130 cargo plane, sent to observe the sinking, dropped a buoy to monitor for any possible pollution.

The Coast Guard warned mariners to stay away, and aviation authorities did the same for pilots.

In about four hours, the ship, its hull pockmarked with holes, vanished into the water, said Chief Petty Officer Kip Wadlow in Juneau. It sank into waters more than 6,000 feet deep, about 180 miles from land, the Coast Guard said.

Officials decided to sink the ship rather than risk the chance of it running aground or endangering other vessels in the busy shipping lanes between North America and Asia.

The ship had no lights or communications system, and its tank was able to carry more than 2,000 gallons of diesel fuel. Officials, however, didn't know how much fuel, if any, was aboard.

A light sheen and some debris were visible as the vessel sunk. Officials expect the sheen to quickly dissipate.

The ship was at Hokkaido, Japan, and destined for scrapping when a magnitude-9.0 earthquake that struck the country in March 2011 triggered a tsunami. The waves dislodged the vessel and set it adrift

In total, about 5 million tons of debris was swept out to sea.

The boat did not have any cargo aboard, Coast Guard spokesman Paul Webb said. He said he didn't know who owned the Ryou-Un Maru, which had been traveling about 1 mph in recent days.

As the Coast Guard was readying to fire on the vessel, a Canadian fishing vessel, the 62-foot Bernice C, claimed salvage rights over the ghost ship in international waters.

Plans to sink it were halted so the Canadian crew could have a chance to take the stricken ship. A Canadian official with knowledge of the situation told The Associated Press that the Bernice C was unable to tow it.

The Canadian boat left and, once it was about 6 miles from the Japanese vessel, the Coast Guard began to fire, first with 25 mm shells, then a few hours later with ammunition twice that size.

In the year since the tsunami, the debris from Japan has washed up on shores across the Pacific.

In January, a half dozen large buoys suspected to be from Japanese oyster farms appeared at the top of Alaska's panhandle and may be among the first tsunami debris.

State health and environmental officials have said there's little need to be worried that debris landing on Alaska shores will be contaminated by radiation. The earthquake triggered the world's worst nuclear crisis since the Chernobyl accident in 1986.

State officials have been working with federal counterparts to gauge the danger of debris including material affected by a damaged nuclear power plant, to see if Alaska residents, seafood or wild game could be affected.

D'Oro reported from Anchorage, Alaska. Associated Press writers Rob Gillies in Toronto, Dan Joling in Anchorage and Whitney Phillips in Phoenix contributed to this report.