PORTLAND, Oregon (Reuters) - A huge dock unmoored during last year's Japanese tsunami washed up on an Oregon beach this week and authorities are debating how to remove it.

"This is the first object that has washed up that was unique enough to confirm that it was, indeed, from the tsunami," Chris Havel, spokesman for the Oregon Parks and Recreation Department, said on Wednesday.

The Japanese consulate confirmed Wednesday that the dock is from the tsunami. "It is from some area on the Northeast coast of Japan," Havel said.

Oregon is working with other West coast states, the Federal government, non-profits and others to coordinate cleaning up the debris. Japan has estimated that as much as 1.5 million tons of debris could still be afloat.

The 66-foot-(20-metre-) long dock is made mostly of concrete and metal, with a small metal plaque with Japanese writing attached.

It washed up early on Tuesday morning on scenic Agate Beach, just north of Newport, Oregon, about 110 miles southwest of Portland.

Oregon is moving ahead with removal, although there are questions about who should pay for it.

"We will bear the cost right now," Havel said. "But in an unusual event like this, is there some other way to cover it? We don't really know at this point."

Authorities are considering the best way to remove the dock from the beach, Havel said, and are considering dismantling it on the beach or pulling it back out to sea.

The dock tested negative for radiation, which was a concern because of the major radiation release at the Fukushima Daiichi nuclear power plant following March 2011's 9.0 magnitude earthquake.

That temblor caused a tsunami that killed nearly 16,000 people and left over 3,000 missing on Japan's main island of Honshu.

The catastrophe swept an estimated 5 million tons of debris out to sea, but most of it sank.

Everything from soccer balls and buoys to building materials has floated across the Pacific and washed up on shores across the U.S. West Coast.

Authorities are concerned about removing the debris, the possibility of animals ingesting junk, toxins and the spread of invasive species.

The Parks Department is working with Oregon's Department of Fish and Wildlife to contain any invasive species threats, Havel said.