A tour boat with as many as 26 people aboard went missing in rough and cold waters off northern Japan on Saturday after issuing a distress call and reporting to be sinking, news agency The Associated Press said.

AP reported that no survivors have been found after more than seven hours of an intense search involving six patrol boats and four aircraft.

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

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.

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

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

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Prime Minister Fumio Kishida, who was attending a two-day water summit in Kumamoto in southern Japan, was cancelling his program for Sunday and was set to return to Tokyo to deal with the missing boat, the NHK public broadcaster reported.

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.

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

According to the operator’s website, the tour takes about three hours and offers a scenic view of the western coast of the peninsula, including nature and animals such as whales, dolphins and the brown bear.

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The national park is listed as a UNESCO World Heritage site and is famous as the southernmost region to see drifting sea ice.