Over 80 people were injured – some seriously – after a ferry collided off a Japanese island with what appears to have been a whale.

The incident occurred off Sado Island and left at least five people with serious injuries after the supposed whale caused a 6-inch crack at the ferry’s stern.

The ferry was carrying 121 passengers and four crew members.

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A marine expert was quoted by Japanese public broadcaster NHK saying that the ferry must have collided with a whale, according to the BBC.

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Ferry operator Sado Steam Ship Co. said in a statement that the jetfoil ferry reached its destination despite the incident and apologized to the customers, saying the ship was hit by “marine life.”

“My throat hit the seat in front of me,” one passenger told Japanese media, according to the outlet0. “People around me were moaning [in pain].”

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Coast guard officials said the exact cause of the accident is now under investigation.

The Associated Press contributed to this report.