Kai McKenzie was catching waves at North Shore Beach, near Port Macquarie on the NSW mid-north coast, when he was attacked by a suspected three-metre white shark on Tuesday morning.
After paddling to shore, the 23-year-old was saved by a quick-thinking off-duty police officer who used his dog's leash to stem the bleeding.
The surfer's severed leg washed ashore where it was put on ice by a growing crowd of onlookers, NSW Police said.
Beaches in the area were closed after the attack but have since reopened, lifesavers confirmed. (Bianca De Marchi/AAP PHOTOS)
Mr McKenzie and the leg were both airlifted to hospital, amid hopes that surgeons might be able to reattach the severed limb. It has not been revealed if the surgery was successful.
After assessing photographs of the injuries, NSW government shark biologists believe a three-metre white shark was involved in the attack and inflicted "severe injuries" to the surfer's right leg.
Mr McKenzie spotted the shark and tried to fight it off, NSW Ambulance Hastings South acting duty manager Kirran Mowbray said.
"Then he's caught a wave into shore, which is a pretty courageous thing to be able to do," she told reporters on Tuesday.
Initial beach closures have ended, Port Macquarie Hastings ALS Lifeguards said in a statement on Wednesday.
A GoFundMe page organised by Mr McKenzie's neighbour, Lauren Mac, said the young surfer was at John Hunter Hospital, noting it would be a "long road to recovery".
"He saw the shark approach and was able to fight it off but suffered a severed right leg," the page reads.
"Clinging to life, he was able to catch a wave back to the beach."
More than $70,000 had been raised on Mr McKenzie's behalf since the page was set up on Wednesday morning.
His aunt Michelle McKenzie said the young man was "an incredible surfer, skater, musician, videographer and all-round legend".
"He has always lived life to the fullest squeezing every minute out of the day," she wrote in a Facebook post on Wednesday afternoon.
"Yesterday he was attacked by a shark at Port Macquarie, doing what he loved ... he suffered life changing injuries."
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The accomplished surfer, who had several sponsors, was only recently back in the water after suffering a significant injury.
"So happy to be back surfing after having a fractured neck," he posted on Instagram in January.
North Shore Beach is isolated and largely accessible only by a dirt road.
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