TOKYO >> The Japanese Coast Guard said Sunday that rescue helicopters found four of the 26 people from a tour boat missing in the frigid waters of northern Japan since the day before, but their conditions are unknown.

The four people were found near the tip of Shiretoko Peninsula, but the coast guard said it could not confirm whether they were rescued alive. NHK public television said they were unconscious.

Footage on NHK showed one of the rescued people arriving on a helicopter and being transferred to an ambulance on a stretcher, while rescuers held up blue plastic shields for privacy.

The boat carrying 24 passengers and two crew members had gone missing after sending a distress call Saturday, saying it took on water and was beginning to sink.

Sunday’s rescue came after nearly 19 hours of intense search involving six patrol boats, several aircraft and divers. The coast guard said the search continued through the night.

The 19-ton Kazu 1 made an emergency call in the early afternoon, saying the ship’s bow had flooded and it was beginning to sink and tilt while traveling off the western coast of Shiretoko Peninsula near the northern island of Hokkaido, the coast guard said.

The tour boat has since lost contact, according to the coast guard. It said the boat was carrying 24 passengers, including two children, and two crew.

Average April sea temperatures in Shiretoko National Park are just above freezing.

An official for the vessel’s operator, Shiretoko Pleasure Cruise, said he could not comment because he had to respond to calls from worried families of the passengers.

Prime Minister Fumio Kishida, who was attending a two-day summit in Kumamoto in southern Japan, canceled his program for the second day and returned to Tokyo. He told reporters in the early hours of Sunday that he instructed officials “to do everything they can for the rescue.”

The cause of the accident is still under investigation, but experts suspect the boat ran aground and was damaged.

High waves and strong winds were observed in the area around noon, according to a local fisheries cooperative. Japanese media reports said fishing boats had returned to port before noon because of the bad weather.

NHK said there was a warning for high waves of up to 3 meters (9 feet).

A tour boat crew belonging to another operator told NHK that he warned of rough seas when he spotted the Kazu 1 crew and told them not to go. He also said the same boat went aground last year and suffered a crack on its bow.

Yoshihiko Yamada, a Tokai University marine science professor, said the boat was likely to have run aground after it was tossed around in high waves and damaged, flooded and probably sank. A tour boat of that size usually does not carry a life boat, and passengers possibly could not escape a rapidly sinking vessel with its windows likely closed to shield them from strong winds.

In an interview with TBS elevision, Yamada said there was also a slight possibility the boat could have been hit by a whale.

The cold temperature and strong wind could cause hypothermia and put the passengers in severe conditions for survival, according to Jun Abe, vice chairman of the Society of Water Rescue and Survival Research. “It’s a very severe condition especially when they are wet,” Abe told TBS.

According to the operator’s website, the tour takes around three hours and offers scenic views of the western coast of the peninsula and includes potential sightings of animals such as whales, dolphins and brown bears. The national park is listed as a UNESCO World Heritage site and is famous as the southernmost region to see drifting sea ice.