A North Korean boat collided with a Japanese fisheries agency patrol vessel in the Sea of Japan Monday, sending around 20 North Koreans overboard, the coast guard said.
"We are dispatching rescue boats and aircraft to the area, but we don't know any more details about it," Japan coast guard spokesman Kazuma Nohara told AFP.
The North Korean boat was believed to be a fishing vessel, which reportedly capsized partially after the crash. There was no immediate word on the status of the crew.
The collision occurred in waters some 350 kilometres northwest of Noto peninsula in Ishikawa prefecture in central Japan, Nohara said.
"We've been strengthening patrols around the water there in cooperation with the fisheries agency," in recent years following reports that many North Korean fishing boats were poaching fish and squids, he said.
Experts say some fishermen from the North are travelling far out to sea in order to satisfy government mandates for bigger catches.
And dozens of North Korean fishing vessels wash up on Japan's coast every year.
But their old and poorly equipped vessels are prone to mechanical faults and other problems, including running out of fuel, and there are few ways for them to call for rescue.
Boats have also washed up on Japanese shores with the crew on board dead -- referred to as "ghost ships" by local media.
In 2018, 10 North Koreans rescued from a tiny wooden boat drifting off northern Japan were deported back to their country.