Police say a tinny crashed into a harbour marker in Runaway Bay, a suburb on the Gold Coast, about 5am on Friday.

The impact threw one man overboard but trapped another man in the boat before it crashed into a moored catamaran.

Catamaran skipper David Crossley said he was woken by a roaring engine before he heard a bang.

“I ran up on the deck and (the boat) was going around and around in circles,” he told reporters on Friday.

The captain initially thought the tinny was unmanned while it spun out of control but then saw an injured man on board.

Mr Crossley said he jumped in his dinghy and towed the tinny to South Stradbroke Island, raising the alarm with emergency services.

The 36-year-old man who had been thrown from the boat managed to swim to shore and was found at Paradise Point by emergency services while the 34-year-old man was treated at South Stradbroke Island.

Both were taken to Gold Coast University with serious arm and leg injuries, with media reporting one of the men was in an induced coma.

Police are still searching the water after receiving unconfirmed reports two people remain missing.

“We’ve got conflicting versions,” Gold Coast Water Police Senior Sergeant Peter Venz told reporters on Friday.

“The gentleman that was onboard the vessel stated there were four people on board.

“The person who was ejected into the water says there were two people.”

The investigation is continuing.