Ten people found so far from a Japanese tour boat missing off the country's northern coast have been confirmed dead, the coast guard said on Sunday.
The boat went missing on Saturday with 26 people on board during a cruise off the main northern island of Hokkaido.
Of the 10, seven were men and three were women, the coast guard said in a bulletin.
There were 24 passengers, including two children, and two crew members on board.
Drift ice can be seen in area waters as late as March, and water temperatures now would be 2 to 3 degrees Celsius, said an official at a local fishery cooperative.
"Just a few minutes in that sort of water would start clouding your consciousness," he said.
Authorities were using aircraft and patrol boats, including seven ships, three airplanes and four helicopters from the coast guard, to search for the passengers and crew of the "Kazu I" after it ran into trouble off Shiretoko peninsula, famous for its wildlife and dramatic coastline.
The coast guard heard from the crew on Saturday afternoon that water was flooding the vessel. It was last heard from around two hours later, when it contacted its operating company to say it was keeling at a 30-degree angle, Kyodo news reported.
The coast guard said it was not clear what had happened to the boat. No one was available for comment at the company.