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Glen Folkard was surfing on Wednesday afternoon when he was attacked by what is believed to be a bull shark.
He suffered serious injuries to his upper leg and torso as the shark struck, taking a large chunk out of his board.
Eyewitness Steve Tidey says Mr Folkard did not panic, but instead alerted nearby surfers to his plight.
"He yelled out I've been hit, I'm in trouble," he recalled.
"We saw him trying to struggle back onto his board, and the trail of blood."
Lake Macquarie Council lifeguards treated Mr Folkard for his injuries before he was rushed to Newcastle's John Hunter Hospital in a serious condition. He underwent surgery overnight.
The local council says lifeguards will assess the beaches this morning to determine when they can reopen.
Witnesses described how, as Mr Folkard trailed blood, the shark appeared to circle, possibly readying itself for a second attack.
"It was definitely coming around again, you could see the fin and he [the shark] looked ready to attack," surfer Tony Constance said.
Another witness, Tony James, told the Newcastle Herald: "It's just hit him and took him under for a bit.
"He's managed to get to the surface but I saw it start to follow him."
One might think about a shark repellent, a biodegradable oil or chemical that turns away the man eater. Or, perhaps a sound device hidden inside a surf board that sends out an annoying signal within 20 feet that causes the shark to get irritated. Or put it in a waterproof band the surfer wraps around an ankle.