A 32-year-old man is in a critical condition after being bitten by a shark at Lighthouse Beach, near Ballina on the New South Wales north coast, police say.

Officers said the man suffered significant leg injuries after he was bitten by a shark while bodyboarding with two friends, just after 10:00am.

His friends helped him to shore and contacted emergency services.

Paramedics treated the injured man on the back of a ute in the beach car park before he was flown by helicopter to Gold Coast Hospital.

A surfer in the water at the time of the attack said he paddled back to shore as quickly as he could to try and help.

"All I could see was a lot of blood on the blanket that was wrapped around his leg," he said.

"His mate who brought him in, he was in shock.

"He just said it took forever for them to come and get him," the witness said.

Sixteen-year-old Peter Edmonds from Wollongbar was killed when he was attacked by a shark while bodyboarding with a friend at the same beach in 2008.

Earlier this year, Japanese surfer Tadashi Nakahara, 41, was attacked and killed at nearby Shelly Beach.

A large shark was sighted off Lighthouse Beach following the attack. ( Twitter: Nine News Sydney )

Ballina resident and witness Allan Everson told ABC North Coast NSW he called Triple-0 after seeing a man waving for help in the water.

"When I got there, the two young guys who brought him in were holding onto him and trying to help him," Mr Everson said.

"He lifted his head up, so he was still alive, but when I saw his injuries I said 'you better get the helicopter here fast'."

Locals traumatised as junior surf meet looms

Ballina Mayor David Wright said a large shark was seen in the area around the time of the attack.

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"I've been told by one of the policemen that they actually saw a large shark," he said.

"It appears that they've got some part of the shark, a tooth or something like that, and they think it's a [Great] White.

Cr Wright said he spoke to some of the men who helped pull the man to shore, and he recognised one of them as having assisted Mr Nakahara in February.

"I've spoken to the young man who was in the water with the victim, but I didn't ask him too many questions because he was too traumatised," Cr Wright said.

"Having been through it with seven or eight guys all traumatised last time... one of the guys that actually walked up was the fellow that gave mouth-to-mouth to Tadashi in February and he's still an absolute mess, so I didn't want to do anything to exacerbate their condition."

The mayor also said a junior surfing competition was due to start at Ballina tomorrow.

However, all beaches within the Ballina Shire are closed for the next 24 hours, including Lighthouse Beach.

Local lifesavers are conducting patrols of the area.

The beach has a reputation for attracting bull sharks when the water is dirty.