Kai McKenzie, a 23-year-old surfer, was attacked by a suspected three-meter shark while surfing at North Shore beach near Port Macquarie on Tuesday morning.

Despite the attack, McKenzie managed to fight off the shark and catch a wave back to shore.

Onlookers and an off-duty police officer used makeshift tourniquets, including a dog leash, to stem the bleeding from his severed leg.

The severed leg was later retrieved from the beach and put on ice by locals.

McKenzie and his leg were airlifted to the hospital, with hopes that surgeons might be able to reattach the limb.

It has not been revealed if the surgery was successful.

NSW government shark biologists believe a three-meter white shark was involved in the attack and inflicted severe injuries to McKenzie's right leg.

Kirran Mowbray, the acting duty manager of NSW ambulance service Hastings South, said McKenzie was recovering in hospital in a serious but stable condition.

She praised the off-duty police officer for using the dog leash as a tourniquet, which essentially saved McKenzie's life until paramedics arrived.

McKenzie was initially taken to Port Macquarie base hospital and later transported to John Hunter hospital in Newcastle.

Mowbray described McKenzie as calm and able to talk to them, calling him a brave and courageous young man.

McKenzie, a sponsored surfer, had only recently returned to the water after suffering a significant neck injury.

He had posted on Instagram in January about being happy to be back surfing after having a fractured neck.

Well-wishes for McKenzie poured in from surfing publications, with Tracks sending their thoughts to 'Kai and his loved ones during this difficult time' and Surfer Magazine wishing him a speedy recovery.

A fundraising page established to assist McKenzie's family with rehabilitation and medical expenses had attracted more than $70,000 since it was set up on Wednesday morning.

His aunt, Michelle McKenzie, described him as an incredible surfer, skater, musician, videographer, and all-round legend who always lived life to the fullest.

North Shore beach is isolated and accessible by a dirt road.

There had been several shark sightings to the north of Port Macquarie in the preceding days.

A tagged great white shark was detected at multiple locations at Sawtell, near Coffs Harbour, on Monday and Tuesday.

Life-savers evacuated the water at a local beach after sighting an unidentified 2.

5-meter shark on Monday.

BiteMetrix, a website that provides surfers with data on increased risk of shark-human interaction, noted a continued increase in great white shark activity in the area during the past week.

The incident came after an attack on a 44-year-old surfer south of Port Macquarie last year, who was saved by an off-duty emergency department doctor.