A Japanese surfer has become the sixth shark fatality in Australian waters in 12 months after having his legs bitten off.

The shark is believed to have come up behind Tadashi Nakahara, biting on both his lower legs and half his board off Shelly Beach, near Ballina on the NSW north coast.

A friend of Mr Nakahara was paddling back out when he heard his mate’s screams just before 10am on Monday.

 ·Sydney siege victims relive their horrific ordeal

Mr Nakahara, 41, was pulled onto the beach by a group of surfers but died at the scene.

Sydney Aquarium shark keeper Nick Harris says an average of six or seven shark attack fatalities occur every year worldwide with most deaths happening in Australia.

Detective Inspector Cameron Lindsay praised those who tried to help Mr Nakahara as his blood poured into the water.

“(Their) actions are commendable,” Insp Lindsay told the Nine Network.

“They took to rescue this surfer … they did their best.”

Tadashi Nakahara was a keen surfer who sold boards in the Northern Rivers region of NSW. Photo: Facebook

Authorities are scouring nearby waters for the shark and Mr Nakahara’s remains.

The victim was surrounded by about a dozen people in the water when the attack occurred.

Friends of the victim told local cafe owner, Karen, the shark came out from nowhere.

“It just came up between a bunch of surfers,” she told AAP.

“They weren’t even that far out.”

Mr Nakahara’s friends were shaken and looked “white as a ghost” as they carried their mate’s board away from the beach, the local said.

One man told the Northern Star he had surfed with Mr Nakahara many times and had known him for about three years.

“I’ve been grieving ever since I heard,” he said.

Ballina Mayor David Wright said the shark was “cruising around” the area.

“I’m a sort of supporter of sharks but something has to be done about this one,” he told the Seven Network.

Surf Life Saving NSW officers and lifeguards have cleared the area and closed beaches between South Ballina and Lennox Head.

The attack comes a day after another surfer was bitten by a shark at Seven Mile Beach, near Byron Bay, 25km north of Ballina.

The 35-year-old man was sitting on his board about 60m off the beach and the father of one is now recovering in Gold Coast Hospital.

-AAP