A Japanese fishing boat washed across the Pacific following the 2011 tsunami has been confirmed as the first piece of debris to reach the coast of California, officials said Friday.

The 20-foot (six-meter) skiff, found this month near the northern Californian coastal town of Crescent City, belonged to the Takata High School in the Japanese city of Rikuzentakata, in Iwate Prefecture.

Japan's consulate in San Francisco helped the US National Oceanic and Atmospheric Administration confirm where the boat came from, after it was spotted washed up on a local beach.

The boat was covered in pelagic gooseneck barnacles. Experts at California's Humboldt State University also helped to identify it, said NOAA spokeswoman Keeley Belva.

The vessel is the 27th item of debris so far confirmed on the US West Coast, and the first in California. Other items have been found washed up in the states of Alaska, Washington and Oregon further up the coast.

One of the biggest items so far, a 66-foot floating dock, washed up in June in Oregon, after a 15-month trip across the Pacific from the port of Misawa, in Japan's Aomori prefecture.

A year ago, the US Coast Guard fired on and sank a deserted Japanese "ghost ship" off the coast of Alaska, after it was deemed to be a potential danger to shipping.

Japan last month marked the second anniversary of the March 11, 2011 9.0-magnitude earthquake that sent a huge wall of water into its northeastern coast, killing some 19,000 people and triggering a nuclear calamity.

The tsunami created the biggest single dumping of rubbish, sweeping some five million tonnes of shattered buildings, cars, household goods and other rubble into the sea.

An estimated three and a half million tonnes sank immediately, leaving some 1.5 million tonnes of plastic, timber, fishing nets, shipping containers, industrial scrap and innumerable other objects to float deeper into the ocean.