A teenager died after being attacked by a shark in Australia on Saturday, police said, one week after a surfer was fatally mauled in the nation's west.

New South Wales police said they were called to Campbells Beach near Coffs Harbour, about 450 kilometres (280 miles) north of Sydney, after reports of a shark attack.

"A man, believed to be aged 18, was body boarding with friends around 100 metres off shore when he was bitten on the legs by what is believed to be a shark," police said in a statement.

"His friends managed to get him to the beach where he was treated by paramedics. He was pronounced dead a short time later."

An ambulance spokeswoman said the victim had severe leg injuries, but he is understood to have died from a traumatic cardiac arrest following the attack.

Police said the boy was sitting upright on his boogie board off secluded Riecks Point when he was bitten on both legs.

"A struggle has taken place and he has managed to break free," Coffs Harbour police inspector Joanne Reid told Sky News. "It has taken a bit of time to get him to shore and he lost a fair amount of blood on the way."

She commended his friends for going to his aid and bringing him to shore.

"It's just a tragic, tragic incident," she said.

Locals said the sharks were rarely seen in the area and incident had shocked the community.

The death comes just a week after a 35-year-old surfer was killed by a shark near Gracetown, about 270 kilometres south of the Western Australian city of Perth.

Sharks are common in Australian waters but deadly attacks are rare, with only one of the average 15 incidents a year typically proving fatal.

Until last week there had not been a fatality since July 2012 when a surfer was bitten in half off the coast of Western Australia, capping an unprecedented spate of five deadly attacks by the marine predators that sparked calls in that state for a cull.