The Japanese coast guard was searching for crew members who fell into the sea from a wooden North Korean fishing boat that capsized off Japan's northwestern coast, officials said Wednesday.

The coast guard said it dispatched four patrol vessels and two aircraft after receiving information of the capsizing earlier Wednesday.

Officials said the incident occurred near an area called Yamatotai, a rich fishing ground that's also crowded with North Korean poachers.

Chief Cabinet Secretary Yoshihide Suga told reporters that a Japanese fisheries inspection ship received a distress call from another North Korean boat. He said the Japanese fisheries and coast guard patrol boats are jointly searching for the missing.

No further details were available, including the number of crew or why the boat capsized. It was not immediately known if the boat was inside Japan's 200-mile (322-kilometer) exclusive economic zone, where the country has the right to all resources.

Last week, a North Korean boat in the area sank after a collision with a Japanese fisheries boat warning it to leave the Japanese exclusive economic zone. About 60 crew members of the North Korean steel boat were safely rescued by another boat from the North.

Japanese Fishing Agency and coast guard officials said they did not arrest the North Koreans because their boat had sunk and could not obtain proof they were fishing illegally. The area is too deep to retrieve the sunken ship, officials said.

The government plans to release a video around the time of the collision.

Japan has stepped up sea patrols after noticing more North Korean boats as Pyongyang tries to boost fish harvests.