A grey reef shark. Picture\: AFP/ Richard W Brooks

Sydney - A teenager was attacked by a shark while spearfishing off Australia's tropical north coast on Sunday, local media reported.

The 17-year-old boy was spearfishing from a boat with friends about 30 kilometres offshore from the remote mining town of Nhulunbuy, 970 kilometres east of Darwin, when he was attacked, the national broadcaster ABC reported.

He was pulled on board bleeding profusely from a bite on his arm and leg from what was believed to be a reef shark.

His friends bound his wounds and a police vessel with paramedics on board rushed him to the local hospital where it was decided he had to be flown to Darwin for further treatment, the ABC said.

Ambulance official Craig Garraway told the ABC the teen's wounds were significant and he'd lost a lot of blood.

Garraway said shark attacks are rare in the warm tropical waters.