A teenage boy who was attacked by a crocodile desperately fought off the predator after being dared to jump into the river.

Lee De Paauw, 18, managed to punch the reptile to escape its jaws after he was bitten during a late night swim in the Johnstone River in far north Queensland, the Daily Mail reported.

The young man had leaped into the croc-infested water from the wharf on the Innisfail esplanade just before 2.30am on Sunday.

The teenager was dared by his friends to jump into the river before the group pulled him to safety after they rushed to his aid, NT News reported.

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He was taken to Innisfail hospital and then Cairns where he is undergoing surgery for significant injuries. He remains in a stable condition.

Paramedics said despite his severe injuries, the victim's arm is still intact.

Cairns Senior Operations Supervisor Rita Kelly said the crocodile was not seen before the incident but the man's injuries indicated he had been attacked by one.

"We're not exactly sure why he went into the water," Kelly said.

"He is very lucky.

"His arm is still intact, which is very fortunate."

Brenton Gangemi, owner of local wildlife cruises Snapping Tours, said he believed the culprit croc was a three-and-a-half to four metre male saltwater crocodile that had been frequenting the area recently.

Gangemi said the man could also have been attacked by a bull shark as they were common in the river.

Saltwater crocodiles are one of Australia's most dangerous land animals and have been responsible for eight confirmed fatal attacks in Queensland since 1985.

In May 2016 New Zealand-born photographer Cindy Waldron died after she was dragged under water by a 4.3m saltwater crocodile while walking with a friend at Thornton Beach, north of Cairns.

New Zealander Cindy Waldron died after being attacked by a crocodile last year. Photo / via Facebook
New Zealander Cindy Waldron died after being attacked by a crocodile last year. Photo / via Facebook