An oil tanker carrying about 75,000 litres of leftover fuel oil is drifting in rough seas off the coast of the U.S. state of Washington.

The Atigun Pass was being towed to China for scrap metal by a tugboat when the cable connection snapped during a storm.

The U.S. Coast Guard says winds are pushing the tanker toward land at a rate of about three kilometres an hour. They say there's a slight danger that it would blow ashore in the next few days, though they call that a "worst case scenario."

The Atigun Pass
The Atigun Pass

Netherlands-based Smit International, the shipping agent, sent in a Canadian crew of six salvage workers by helicopter who will attempt to board the ship.

They face waves more than five metres high and winds of 40 km/h. So far, two attempts to grab the cable have failed.

The coast guard said the 270-metre long tanker was condemned as unsafe by the Oil Protection Act of 1990 and had been docked in Portland's harbour since 1995.

It said the fuel had hardened into a thick paste over the years so it could not be pumped out before the journey.