Witnesses told police a shark attacked the teen at Wilsons Headland at Wooli Beach, north of Coffs Harbour, just before 2.30pm on Saturday.

Board-riders helped the boy to shore and he was given first aid for serious leg injuries but died at the scene despite efforts to resuscitate him.

Beaches in the area, including Wooli, Diggers Camp and Minnie Water, have been closed.

Police initially said the victim was aged 17, later correcting that to 15, while paramedics had been told he was 16.

"It's a tragedy," NSW Ambulance inspector Scott Acton said.

"No words can describe the scene we were faced with today."

Clarence Valley mayor Jim Simmons said the loss of such a young life was terribly shocking.

He said visitors had flocked to the region for the school holidays and there would likely have been many people in the water.

"What's happened there this afternoon would shake everybody," Mr Simmons told AAP.

"All of our sympathies, from people in the area, go out to the boy's family.

"I just ask people to look out for their safety on the beaches."

It is Australia's fifth fatal shark attack this year.

Last Saturday, a 36-year-old Sunshine Coast man was mauled while spearfishing off Queensland's Fraser Island.

Last month, Gold Coast surfer Rob Pedretti, 60, died after he was attacked at Salt Beach at South Kingscliff in northern NSW.

A shark also killed 23-year-old Queensland wildlife ranger Zachary Robba in April off North West Island in the southern Great Barrier Reef.

Experienced diver Gary Johnson, 57, was killed by a shark near Cull Island in Esperance on Western Australia's south coast in January.

A report will be prepared for the coroner.

Australian Associated Press