At least 80 people have been injured after a ferry collided with what was believed to be a marine animal, possibly a whale, off the coast of Japan.

The incident happened just after noon on Saturday during a short crossing from Niigata, a city on the Sea of Japan coast, to Sado island, the coast guard said.

The public broadcaster NHK said 13 passengers has suffered serious injuries, but none had lost consciousness. Others were being treated for minor injuries.

A 15cm crack was found on the stern of the ferry, which continued its journey and arrived at Sado island about an hour behind schedule. The vessel was carrying 121 passengers and four crew members.

Shinichiro Ikeguchi, the deputy director of an aquarium in Niigata prefecture, told NHK that the scale of the impact suggests that the ferry struck a whale, adding that minke and humpback whales are currently migrating through the Sea of Japan.

Passengers described a “huge impact” the moment the collision occurred. “After the sound of a bang ... my throat hit the seat in front of me,” one of them told reporters, according to the Kyodo news agency. “People around me were moaning in pain.”

The cause of the accident is under investigation by coastguard officials.

There are occasional reports of collisions between high-speed ferries and whales in waters around Japan and South Korea. Ferry companies have attempted to lower the risk by installing devices that emit sounds to deter the animals and altering routes to avoid migrating whales.

The ferry’s operator, Sado Steam Ship, said its crew members instruct passengers to keep their seatbelts fastened throughout the crossing, according to Kyodo.

Associated Press and Agence France-Presse contributed to this report