The US Coast Guard sunk a Japanese "ghost ship" with bursts of heavy gunfire when it drifted into Alaskan waters more than a year after being set adrift by a devastating tsunami.

The deserted trawler, seen as a shipping hazard, was first spotted off the coast of Canada on March 24, having drifted thousands of miles (kilometers) across the Pacific Ocean on the current following the March 2011 tsunami.

The Ryou-Un Maru fishing vessel, which appeared about 180 miles off the coast in 6,000-foot (2,000-meter) deep water, was a significant navigation hazard, officials said.

"It's between 150 and 200 feet long, it's unmanned and unlit and adrift. In the dark, it presents a significant danger to other vessels transiting that area," Sara Francis, a spokeswoman for the Alaska Coast Guard, told AFP.

The Japanese owners of the ship had said they did not want it back. Early Thursday, a Canadian crew had tried to save it, but after a closer inspection they abandoned the idea and the operation to sink the ship began.

The Coast Guard fired an initial salvo of 25 mm explosive rounds, causing the ship to catch fire and list slightly, according to Coast Guard Chief Petty Officer Kip Wadlow, in the Alaskan capital of Juneau.

A second salvo was fired later in the afternoon, he said, and the Coast Guard confirmed the vessel sank at 6:15 pm Thursday (0215 GMT Friday).

It released pictures of the rusty-hulled vessel on fire, with a column of black smoke rising into the air.

The Coast Guard said that there was no risk that pollution from the ship would threaten the pristine Alaskan and Canadian coasts.

"If there is any fuel on board it's expected to be diesel fuel, which will disappear very quickly and pose limited risk to the environment," Francis said.

The boat was the largest piece of debris so far to appear off the US coast after the March 11, 2011 tsunami.

Some 20 million tons of debris have washed up since the disaster, and researchers in Hawaii have developed computer models to forecast its movement and predict where and when it could come ashore.