Rescuers say 10 people who were retrieved from the sea and the rocky coast of a northern Japanese national park had died, a day after a tour boat with 26 aboard apparently sank in rough waters.

The search for the others is still ongoing after the boat sent a distress call on Saturday afternoon saying it was sinking.

The location, near the Kashuni Waterfall, is known as a difficult place to manoeuvre boats because of its rocky coastline and strong tide.

There were two crew and 24 passengers, including two children, on the 19-ton Kazu 1 when it ran into troubles while travelling off the western coast of the Shiretoko Peninsula.

The coast guard said the 10 victims — seven men and three women — were adults.

The Transport Ministry launched an investigation into the boat’s operator, which had two accidents last year.

The ministry said it was looking into safety standards and the decision to conduct the tour despite rough weather on Saturday.

The operator, Shiretoko Pleasure Cruise, had been instructed to take steps to improve its safety following earlier accidents in which it ran aground in June without causing injuries, and another in May, when three passengers suffered minor injuries when the boat collided with an object.

“We will thoroughly investigate what caused this situation and what kind of safety oversight was involved to allow the tour in order to prevent another accident,” Transport Minister Tetsuo Saito, who visited the area on Sunday, told reporters.

Following an intensive search involving six patrol boats, several aircraft and divers that went through the night, rescuers on Sunday found four people near the tip of Shiretoko Peninsula and later six more in the same area. Some of them were plucked from the sea, while others were washed onto the rocky coast.

An orange-coloured, square-shaped lifesaving float with the boat’s name on it was also found near the rocks, the coast guard said.

Footage on public broadcaster NHK showed one of the victims arriving on a helicopter and being transferred to an ambulance on a stretcher. Rescuers held up blue plastic shields to protect the victim’s privacy.

The sightseeing vessel made an emergency call early on Saturday afternoon, saying its bow had flooded and that it was beginning to sink and tilt, the coast guard said. Contact with the boat had since been lost.

Average April sea temperatures in Shiretoko National Park are just above freezing, which experts say would cause hypothermia.

Prime Minister Fumio Kishida cut short his attendance at a two-day summit in Kumamoto in southern Japan and returned to Tokyo. He told reporters early on Sunday that he instructed officials “to do everything they can for the rescue”.