Mike Baird has performed a second policy backflip in as many days, announcing he will pursue a six-month trial of shark nets along NSW's north coast after another shark attack.

After resisting calls to install nets, which kill other marine life, the premier announced the policy change on Wednesday, a day after he reversed a ban on greyhound racing.

The premier says he will lobby the federal government to install shark nets along the state's north coast after a 25-year-old man, named in media reports as Seneca Rus, was bitten at Ballina while surfing with friends on Wednesday morning.

The attack comes less than two weeks after 17-year-old Cooper Allan was mauled by a great white at Ballina's Lighthouse Beach.

Following Mr Allan's attack the state government announced up to 100 "smart" drumlines would be placed along the NSW coastline with the focus on the northern beaches in a bid to keep swimmers safe.

Now, Mr Baird says these drumlines aren't enough.

"Ultimately we get to the point where we have to prioritise human life over everything," he told NSW Parliament.

"Certainly the sentiment in that local community has shifted. It was against nets, no doubt about it. The recent attacks have started to shift that."

About a year ago, Mr Baird wrote about his apprehension over installing shark nets: "While the safety record is great, nets don't just catch sharks, they catch other sea-life too. That reality is a serious concern to all of us."

A recent trial to install eco-friendly barriers around Ballina was scrapped after conditions became too rough.

Primary Industries Minister Niall Blair said the shark nets would add to existing measures, such as tagging programs and aerial surveillance.

"We will be doing everything we can to get those nets, if approved, in the water as soon as possible," he said.

Wednesday's attack has shut down all beaches in Ballina for 24 hours and authorities are trying to determine what type of shark was involved.

Mr Rus told police he first felt a bump on his board before he was attacked and fell into the water.

He was then was taken by friends to Ballina Hospital suffering injuries to his lower right leg.

"Got a good chink out of his shin... he was super lucky," said surfer Scott Crump, who was in the water at the time.

"So rattled....I would have been next in line on the buffet."

There have been six shark attacks at Ballina Shire beaches since January last year, including one that killed Japanese surfer Tadashi Nakahara.