A 17-year-old surfer was attacked by a shark off Australia's east coast on Monday, with locals saying he was lucky his board bore the brunt from a suspected great white.

The teenager, named as Cooper Allen in local media, was bitten on the leg while surfing at Ballina Shire's popular Lighthouse Beach -- the scene of several attacks in recent years.

Fellow surfers rushed to his aid, helping him back to the beach where he received first aid from off-duty nurses.

Surf Life Saving New South Wales said the teen suffered "severe lacerations" but police said his injuries are not considered life-threatening.

"But obviously, with a shark wound, they're always quite severe," New South Wales police chief inspector Nicole Bruce told reporters.

"(He) received lacerations and bite marks to his upper-thigh area, he was assisted into the shore and off-duty nurses treated him.

"We've got the surfboard and the bite marks will be analysed by the DPI (the Department of Primary Industries)."

With school holidays in full swing, police declared beaches across Ballina, some 740 kilometres (460 miles) north of Sydney, closed for 24 hours.

Of the 14 unprovoked shark attacks off the New South Wales coast in 2015, most occurred along a 60-kilometre hotspot from Evans Head to Byron Bay which includes the town of Ballina.

Bruce said it was too early to say what kind of shark was responsible, but a 3.5 metre great white was spotted at Lighthouse Beach by aerial surveillance after the attack. It was chased out to sea by lifesavers on jet skis.

"There has been (a) sighting of a great white, a four-metre shark, further off the shore but no-one actually saw which shark it was that's bitten him," she said.

Efforts to contain the marine predators have so far proven difficult, with a shark eco-barrier trial at Lighthouse Beach and nearby Lennox Head recently scrapped due to rough conditions.

"You can never be in the clear, I suppose, it's just one of those things, you share the water with them, it could happen any day, anywhere," said Bruce.

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Craig Nolan, president of the Ballina Lighthouse and Lismore Surf Lifesaving, told the Australian Broadcasting Corporation the timing of the attack, ahead of the start of southern hemisphere summer, was unfortunate.

But he added: "Apparently the prime attack was on the board, so it took the brunt."

As the injured teenager remained in a stable condition in Lismore Base Hospital, Ballina Mayor David Wright said he understood the shark was a great white and that it had come up from behind.

He said that it had wrapped its jaws around the rear of the surfboard, including its fin, and over the victim's leg. But he said the board had helped prevent more serious injury.

Wright said despite the latest incident, surfers would still flock to the north coast beaches.

"It certainly won't stop surfers," he told AFP.