A second shark attack in two days has taken place on the NSW north coast with a surfer knocked off his board this morning at Lennox Head.

Ambulance paramedics said the 52-year-old man was not injured and they were told the shark swam away after the incident.

Today's attack followed the mauling of a bodyboarder at Ballina, 10 kilometres further south, on Thursday morning.

The 32-year-old man had his legs mauled by what was believed to be a Great White and is reportedly in a critical condition in Gold Coast Hospital.

At the request of NSW Police, the Department of Primary Industries issued a permit authorising the "capture, destruction or possession" of the shark.

However, a police spokesman said officers would not being acting on the permit.

Surfer Buzz Tilley said he was in the water at Lennox Head today when he noticed all the surfers around him had started paddling in to shore.

"A guy from the bank whistled at me and just gave me the fin signal with his hand, so I worked out what was going on," he said.

"I sort of wanted to keep surfing but then I realised I was going to be the only one out there in another 30 seconds."

Mr Tilley said he was not worried about going in the water this morning after yesterday's attack because there were still "pretty good odds" of staying safe.

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"But there's no-one in the water now, so the odds are a bit worse."

Another witness, Robin Mather, said the man's surfboard was clearly damaged.

"We went down [to the shore] and there was a bunch of surfers around him, and [I] just looked at the bottom of his board and one of his fins was missing," he said.

"There was puncture wounds, so like bite marks, all the way through the back there of his board and he looked really shaken up.

"It was really, kind of heavy and he was fine, just looked super rattled."

All beaches in the Ballina Shire area have been closed.

The latest attack took place as an international junior surfing contest was due to get underway at Lennox Head. The Skullcandy Oz Grom Open 2015 has now been postponed following the latest attack.

About 270 of the country's best young surfers were due to take part in the event, which attracts surfers from around the world and is one of the biggest junior competitions in the country.