A Byron Bay man has died after being attacked by a shark at a popular beach at the town on the NSW north coast.

Police have confirmed the man, in his 40s, was a local resident and has been identified by a family member.

He was pulled from the water at Clarkes beach just before 11am on Tuesday in a critical condition.

He was believed to have suffered a bite to his leg, an ambulance spokeswoman said.

Emergency crews were called just after 10.30am (AEST).

A doctor performed CPR on the man but he died at the scene.

Water police were on the way to the incident on Tuesday afternoon.

Surf Life Saving NSW spokeswoman Donna Wishart said Byron Bay beaches had been closed from Tallows in the south to Belongil in the north.

NSW government officers will be brought in to determine the type of shark involved in the attack.

Police will speak to the media on Tuesday afternoon.

NSW Ambulance paramedic Andrew Chapman said the man was bitten above the knee.

“It was a fatal bite with major blood loss. He probably died in the water because there was no blood loss on the beach,” he told News Corp Australia.

Newcastle lawyer Mark Hickey, 52, was one of the first people on the scene and said he saw a six- or seven-foot (1.8-2.1m) shark menacing the victim.

“I saw what looked like seaweed but it was blood in the water,” the tourist told the news organisation.

“The shark came back to him and had another go. I didn’t know it was a person but when I realised I ran out and waded to the bank and grabbed him and did CPR but it was too late.”

Media reports have said the man was swimming when he was attacked.

Beaches from Tallows to Belongil will remain closed for 24 hours.