WELLINGTON (AFP) - A surfer who was attacked by a shark in a New Zealand bay punched it in the face to free himself from its grip, reports said on Saturday.

It was the second shark attack off the southern coast of New Zealand's South Island in recent weeks.

In the latest incident on Friday evening, a 28-year-old man was about 50 metres off shore at Porpoise Bay when the shark seized his leg, leaving three bite wounds from his thigh to his calf.

"He was sitting on his surfboard and the shark came up from nowhere and hit him," fellow surfer Nick Smart told Fairfax Media. "He struggled for a bit and then punched the shark and it let him go."

The man made his own way to shore, where he had to wait about 40 minutes for an ambulance to arrive.

"He was totally coherent and talking. He was definitely in a bit of pain but he handled it really well," Mr Smart said.

Last month a New Zealand doctor, who was attacked while spearfishing off the southern coast, fought off the shark with a knife before heading ashore to stitch his own wounds and then going to the nearest pub for a beer.