HYANNISPORT, Mass. -- Eighteen people were injured when a high-speed ferry struck a jetty in Hyannisport, Massachusetts, and began taking on water, authorities said.

Hyannis acting Fire Chief Dean Melanson said Saturday that 15 people, of the 18 who were injured, were taken to the hospital. The other three people injured underwent evaluations that did not require them to be hospitalized. A Cape Cod hospital spokeswoman said the injured had been treated and released by noon Saturday.

The ferry Iyanough hit the jetty and grounded on the rocks at the Hyannis Harbor entrance around 10 p.m. Friday. It serves a 26-mile route between Nantucket and Hyannis. There were 48 passengers, 6 crew members and 3 food service workers on board the vessel at the time of the mishap.

Passengers reach safety after a ferry hit a jetty in Massachusetts. David Curran

The aircrew airlifted the five injured passengers as well as 10 uninjured passengers who were unable to navigate the slippery rocks. There were 56 people on board, the Coast Guard said in a statement.

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Coast Guard Lt. Cmdr. Matt Baker said in a statement that rough seas, strong winds and slippery rocks impeded the rescue efforts, but all passengers were taken to safety.

The ferry is operated by the Woods Hole, Martha's Vineyard and Nantucket Steamship Authority, connecting the Massachusetts islands with the mainland. It can hold up to 400 people.

Steamship Authority general manager Wayne Lamson says it's not completely clear how the crash happened. Authorities are investigating.