A tour boat with 26 people aboard, including two children, has been missing off northern Japan for several hours with no sign of survivors, the country's coastguard said.

The 19-ton Kazu1 made an emergency distress call on Saturday afternoon, saying the bow of the vessel had been flooded and was beginning to sink and tilt.

The crew also said those on board were wearing life jackets and the boat was keeling at a 30-degree angle.

It was travelling off the western coast of Shiretoko Peninsula, in the northern island of Hokkaido.

There has been no contact from the boat since.

The vessel was carrying 24 passengers, two of whom were children, and there were also two crew members.

Six patrol boats, four aircraft and divers have been sent to the area to search for any survivors.