(CNN) -- A small wooden boat found off the western island of Sado in Japan contained decomposing bodies, according to local police.
The boat was badly damaged and contained faint markings on the side that appeared to be Korean characters, according to the Sado West Police. But the characters were so faint that they could not read it clearly, said Toshiyuki Kojima, deputy chief of Sado Nishi Police Station.
The boat was discovered early morning Wednesday, drifting into a rocky part of the coast at Mano Bay in Sado City. Authorities did not know how long the boat had been there.
Police would not say exactly how many bodies were found on the boat, but said that some bodies had decomposed to the point where only skeletons remained.
Local Japanese media reported five bodies were found.
Last September, a group of nine North Koreans sailed to Japan and was discovered drifting about 15 miles off the coast of Noto peninsula. They resettled in South Korea.
While it's rare for North Korean defectors to sail to Japan, in 2006, four North Koreans floated to northern Japan. In 1987, a family of 11 drifted from North Korea to west Japan.