Tsunami waves generated by the magnitude-9 earthquake in Japan last March dragged between three million and four million tons of debrisinto the ocean after tearing up harbours and homes.

Scientists believe ocean currents are carrying some of the lumber, refrigerators, fishing boats and other objects across the Pacific towards the US.

University of Hawaii senior researcher and ocean current expert Nikolai Maximenko said one to five per cent of the one million to two million tons of debris still in the ocean may reach Hawaii, Alaska, Oregon and Washington and British Columbia.

Some debris appears to have already arrived, like half a dozen large buoys suspected to be from Japanese oyster farms found in Alaska late last year.