A U.S. Coast Guard vessel opened fire Thursday on a fishing trawler in an attempt to sink it after last year's tsunami off Japan left it adrift near Alaska, where it was posing a hazard to other marine vessels.

(CNN) -- A U.S. Coast Guard vessel opened fire Thursday on a fishing trawler in an attempt to sink it after last year's tsunami off Japan left it adrift near Alaska, where it was posing a hazard to other marine vessels.

"The gunneries operation began at 1 p.m.," (5 p.m. ET), said U.S. Coast Guard spokesman Jonathan Lally. "The Coast Guard vessel Ana Kappa, based out of Petersburg, Alaska, opened fire with 25 mm cannons on the Japanese vessel. The time it will take to sink is dependent on the weather conditions in the area."

Observers from a helicopter said it had not yet sunk.

A Canadian vessel, the Bernie C, had expressed an interest in salvage, which delayed the operation, but officials deemed that it would be too unsafe to tow or attempt to salvage the vessel, said Coast Guard spokesman Kip Wadlow.

The rust-stained trawler is part of a giant debris field in the Pacific Ocean generated by the devastating wall of water that struck northeastern Japan after a magnitude-9.0 earthquake on March 11, 2011.

The enormous wave dragged everything from cars to houses out into the ocean, killing thousands of people.

The drifting trawler was considered a hazard to navigation for vessels in the area, according to authorities. Area mariners were informed about the unmanned and unlit boat's presence.

Early Thursday, the trawler was about 170 nautical miles southwest of Sitka, Alaska, the Coast Guard said. A Coast Guard plane dropped a self-locating data marker buoy to track the boat's location.

The trawler was first spotted floating near British Columbia by a Canadian military air patrol, and it was then determined that it had been adrift since the tsunami, Canadian officials said last month.

The Japan Coast Guard identified the owner of the vessel after being contacted by Canadian officials, who were provided the identification number on the hull.

The vessel, which was used for squid fishing, was moored at Hachinohe in the Aomori prefecture when the tsunami hit, Japanese authorities said.

CNN's Tina Burnside, Jake Carpenter and Jethro Mullen contributed to this report.