Ten people found by rescue workers after a tour boat went missing in frigid waters off Japan’s northernmost island have been confirmed dead, the coastguard said.

Authorities continued their search with patrol boats, aircraft and helicopters for the remaining 16 people – including two children – who were onboard the Kazu I when it ran into trouble on Saturday off the Shiretoko peninsula on the northern island of Hokkaido.

Nine of those found were either in the water or on nearby rocks, the coastguard said.

Drift ice can be seen in the sea around the area as late as March, and water temperatures would be around 2C to 3C at this time of year, an official at a local fishery cooperative said. “Just a few minutes in that sort of water would start clouding your consciousness,” he said.

The area is famous for its wildlife and mountains, and boats bring tourists along the coast to spot brown bears.

The Kazu I crew alerted the coastguard on Saturday afternoon that water was flooding the vessel. About an hour later they contacted the boat’s operating company to say it was keeling at a 30-degree angle, Kyodo News reported.

The coastguard said it was not clear what had happened to the boat. No one was available for comment at the company that operated the Kazu I. High waves and strong winds had been observed around noon on Saturday, Kyodo said.

Kazu I was the first tour boat to operate in the area this season, the news agency said. In May last year it collided with a floating object, injuring three people, and in June it ran aground in shallow water shortly after leaving port, Kyodo said.