Image caption The boat was washed ashore near an island off Japan

Five bodies have been found in a badly damaged boat with Korean language markings off Japan's west coast.

The 10m vessel washed ashore on Sado Island, Niigata City in waters between Japan and the Korean peninsula.

All those on board were adult males, Japanese broadcaster NHK said. Police have not confirmed their nationalities but suspect the men were North Korean.

In the past a very small number of North Korean refugees have made the journey to Japan by boat.

Local fishermen found the vessel, weighing more than 4,500kg, around 09:00 local time (17:00 GMT), police say.

The fishermen told local media that they found no engines attached to the boat. The men on board were estimated to have died at least a month ago, police added.

In September last year, a boat carrying nine North Koreans arrived in Kanazawa, further to the south. The group were later resettled in South Korea.

In January 2012 another group of four North Korean fishermen found by the Japanese coastguard after developing engine trouble were repatriated at their request.

A police spokesman told AFP news agency that the Korean characters on the boat - which appeared to have been drifting for some time - were impossible to read.

"The bodies are decomposed badly," the spokesman added.