The sharks, including two about four metres long, were spotted close to where Mike Wells was grabbed during a twilight surf at North Avoca Beach on Tuesday.

The 28-year-old told paramedics he felt his arm being pulled under his bodyboard.

Mr Wells punched the shark, which was about two metres, forcing it to let go.

He was treated at Gosford Hospital for bleeding, a five-centimetre cut to his right forearm and puncture wounds to his right wrist.

Mr Wells, a surf shop worker, was attacked within sight of the house he rents with his girlfriend, Samantha.

She said yesterday that he was doing well. A Gosford Hospital spokesman confirmed Mr Wells had been discharged yesterday afternoon.

On a surfing blog a friend, Grant Molony, said he was "cracking jokes [and was] a lucky man with a story to tell for years to come".

Although the species that attacked Mr Wells had not been identified, locals reported seeing a bronze whaler shark on Monday.

His neighbour, Max, said people walking on the beach rushed to his aid when he came ashore. His board strap was used as a tourniquet and a towel covered huge gashes.

His girlfriend ran up the beach screaming and asked Max to call an ambulance. "He was as white as anything but still lucid," Max said.

Westpac Lifesaver Rescue Helicopter chief Stephen Leahy said two "very large" sharks were spotted off Copacabana. Others were seen off Avoca and Terrigal.

"There are a number of schools of baitfish, which is common for this time of year, and sharks are chasing these fish," he said.

He was unable to say what species of shark his crew saw.

Surf Life Saving NSW spokesman Dean Storey said the odds of being attacked were small but urged swimmers to stay between the flags.

Mr Storey said more sharks were being spotted because there were more people in the water and more baitfish were around.

"If people are concerned about sharks they should swim between the red and yellow flags because they and the water around them will be under constant surveillance," he said.

Avoca beach was closed yesterday as a precaution.

Surfwatch Australia director Michael Brown has told the Newcastle Herald shark populations along the Hunter and Central Coast were tipped to boom due to nutrient-rich water, plentiful baitfish and warmer currents.

One surfer at North Avoca, Lachlan Taylor, 19, went surfing at 8am yesterday, and saw masses of fish leaping.

"Then I saw a huge shadow so I just absolutely bolted," he said. with SMH