A large, rusting ghost ship floating aimlessly off the Pacific coast is drifting toward Alaskan waters, setting off a series of tactical steps by the U.S. Coast Guard.

The unmanned 54-metre fishing vessel is at the forefront of tonnes of debris heading across the Pacific Ocean from last year's massive tsunami in Japan.

The ship is about 150 kilometres west of the northern-most tip of Haida Gwaii, or the Queen Charlotte Islands, off British Columbia's coast and appears to be heading north.

U.S. Coast Guard Petty Officer 1st Class David Mosley said Sunday the coast guard dropped a data marker on the ship Saturday so they would have a constant, real-time position on the ship.

While British Columbia's shores now aren't likely to be the ship's destination, Mosley said, the key concern is whether the ship moves northwest over top of Haida Gwaii and into the body of water that divides Canada and the United States.

"Dixon Entrance … is a pretty heavily travelled area for cargo ships, fuel ships, even cruise ships in the summer, so we have to be aware of what the overall danger is to the maritime traffic as well as the maritime environment," he said.

Warning to mariners

"It has the potential to be a hazard, especially with the unknown of what's on board, the direction that the vessel could be travelling."

In Canada, several government ministries are watching the drifting vessel, including Transport, Environment, Fisheries, Public Safety and National Defence.

A Transport Canada spokeswoman said marine currents and winds could make the vessel's destination unpredictable; a warning has been issued to mariners to watch for the potential hazard.

"We will ensure that it does not wash ashore on the Canadian coast," Sau Sau Liu said.

The vessel was swept out to sea along with an island of other debris when the tsunami hit Japan after the magnitude-9 earthquake struck last March.

On northerly course

Officials say the ship is a former squid fishing vessel that was based in Hokkaido, Japan. At first officials thought the ship, which is near the Oshawa Seamont, was bound for Canadian waters, but Mosley said it now appears to be on a northerly course.

"All that superstructure up above the water line acts like a sail on a sailboat: If it's a good northerly wind, it will push it," he said. "Depending on the direction it goes, that's the window of time we have to respond to operate and ensure the safety of commercial vessels and the environment."

Mosley said a U.S. Coast Guard cutter would be sent out this week to assess the condition of the vessel.

"So we're looking at — do we work with other government agencies to go out and just sink it while it's still well off shore, or do we need to arrange to have a vessel come out and take it into tow and dispose of it in a way other than just going out and scuttling it. Those are all different things we have to look at."

In Old Massett, B.C., John Disney wondered about the fate of the crewless vessel, despite assurances from federal authorities. The economic development officer is worried about things such as whether there's radiation aboard given what happened to a nuclear reactor in Japan.

"I would dearly love to get on that boat and get some swabs off it, and run 'em through our testing equipment," he told CBC News. 

With files from CBC News