A paddle boarder had part of his hand bitten off as he attempted to fight off a shark on the NSW north coast.

The 29-year-old man also suffered a deep gash to his thigh when he was attacked by what is believed to be a bull shark at Diamond Head, about 50 kilometres south of Port Macquarie, at 10.45am on Friday.

A NSW Ambulance spokeswoman said paramedics arrived to find a 29-year-old man, who is believed to be from the Central Coast, with shark bites to his hand and thigh.

"The man lost his index finger and knuckle as a result of the attack," the spokeswoman said. The victim was flown by helicopter to John Hunter Hospital for treatment.

News reports said the man, who was camping at Diamond Head with family and friends, was surfing with friends when a pod of dolphins came through the waves. About 10 minutes later, he was attacked.

The shark hit him three times and it is understood he was injured trying to fend off the animal. He was assisted from the water by friends.

The beach where the attack occurred is located within the Crowdy Bay National Park, and close to the Kylies Beach campground. The NSW National Parks and Wildlife Service says on its website that the beaches in the national park are "crowd free".

Adam Eady, from the Crowdy Head Surf Life Saving Club, south of the attack site, said beaches from Crowdy Head to Camden Haven to the north had closed as a precautionary measure.

Surf Life Saving NSW spokeswoman Donna Wishart said the attack occurred at an unpatrolled beach in a "reasonably remote location".

"He was surfing on a stand-up paddle board when the shark bit him on his left thigh," she said.

"He also sustained injuries to his hand trying to force the shark away. Ambulance officers have treated the man at the scene."

A shark expert from the NSW Department of Primary Industries is believed to be travelling to the area, she said.

Dean Storey, Surf Life Saving NSW Lifesaving Manager, said shark attacks were very rare and people were at far greater risk of drowning.

He said there had been five coastal drownings in NSW in December.

"Holidaymakers who are concerned about sharks should stick to swimming at patrolled locations," he said.

"That way lifesavers and lifeguards can clear the water in the event of a shark sighting and first aid support and equipment is immediately available."