Diver stabbed in chest by stingray

File photo.

A man pierced by a stingray barb in the Hauraki Gulf has been helicoptered to Auckland Hospital.

The man was scuba diving near Pakatoa Island when he was attacked by the stingray at about 1:30pm.

Westpac Rescue Helicopter advanced paramedic Chris Deacon says the man didn't notice the stingray and swam over the top of it.

His injuries were moderate.

Paramedics delivered first aid and transported the man to hospital for testing and treatment just before 3pm.

According to experts, stingrays do not normally attack humans.

"It's virtually unknown for stingrays to go on the attack," said Leigh Marine Laboratory's operation manager Arthur Cozens.

Mr Cozens said stingrays use their barb as a "defensive mechanism".

"If you just happen to be perceived as a threat, up goes the tail," he said.

Mr Cozens said most stingray injuries result from people standing on the sea creature's barb in dirty water.