A man was knocked unconscious and three others suffered facial fractures and broken ribs after a whale slammed into a charter fishing boat off Australia's north coast, the skipper said Monday.

The 30-foot (9-metre) vessel was returning to port in the Whitsundays off the Queensland state coast with eight passengers on board when a humpback whale rammed it from below, sending it airborne.

"Within a split second we all hit the floor, the boat launched up into the air and it dislodged everyone off their feet," captain Oliver Galea told AFP of the drama on Saturday. "None of us knew what happened."

A 71-year-old South African man was knocked out and tended to by the boat's crew while they alerted emergency services. A helicopter escorted the boat to shore where four men were sent to hospital.

The tourist was treated for a broken nose, while Galea needed eight stitches for a nasty head wound. A third passenger suffered facial fractures and another broken ribs.

"We see whales all the time, but it's never (been) known for this sort of thing to happen," Galea said, adding that some of the passengers spotted what they believed to be a humpback in the water after the accident.

Each year humpback whales migrate north from the Antarctic to the warmer climate off Australia's coastline to mate and give birth. They can grow up to 16 metres (52 feet) long.

The ordeal has not deterred any of the passengers, Galea said, who were "all in good spirits" after they got together Sunday to eat their previous day's catch.

"The main thing is we all got home, and we have a few battle scars to show," he added.