Fate of those on board the fishing boat remains unknown as Japanese coastguard and patrol boat search Sea of Japan.

Japanese authorities were searching on Wednesday for a North Korean fishing boat that was reported to have sunk in the Sea of Japan.

A North Korean boat telephoned a Japanese fishing office to report that another North Korean vessel had sunk in the northern part of a rich fishing ground known as the Yamato Shallows, a spokesman for the Japanese coastguard said.

The fate of those on board was not known.

But an NHK report said earlier on Wednesday that a crew of a North Korea ship “fell” overboard. It was unclear if the Japanese broadcaster was referring to one or more members of the crew, or the vessel’s entire crew.

The coastguard and a patrol boat from Japan’s Fisheries Agency have begun a search, the spokesman said, adding that it was not known why the boat had sunk.

The incident took place in the same area in which a Japanese patrol boat and a North Korean fishing boat were involved in a crash this month, while the patrol boat was chasing the North Korean boat off Japanese waters.

Japan rescued about 60 North Korean crew members in that incident, after the fishing boat sank.