Bite marks and a single shark tooth were left in the man's surfboard as a result of the attack.

A 25-year-old surfer has escaped with his life after being attacked by a shark in Northland - and he has a souvenir to prove it.

Lodged near the tip of man's board was a shark tooth and an impressive-looking bite mark, which an expert believes belongs to a great white shark.

Pictures taken at the scene, show a wet-suit clad man getting into the emergency helicopter with a sling around his arm.

Ken Cashin Bystanders watched as the man boarded the helicopter.

The attack happened at Baylys Beach, near Dargaville, at around 6pm on Friday.

The Northland Emergency Services Trust helicopter arrived on scene at 6.41pm, and later transported the man to Whangarei hospital with serious injuries.

Department of Conservation (DOC) marine scientist Clinton Duffy said he could tell immediately what type of shark it was from the photograph of the tooth in the board.

"The tooth is definitely from the lower jaw of a great white shark.

"The whole bite is quite distinctive; the size of the teeth, the spacing and the number of teeth are all characteristic of a great white shark. Very few sharks have jaws as large and teeth as large as a great white shark and they have a relatively low number of teeth in the jaw.

He said the species was relatively common around the Northland coast.

Ken Cashin Emergency services arrived at the remote beach around 6.30pm on Friday.

"I've been involved in tracking them up along that north-west coastline using satellite tags."

He said the attack would most likely have been due to inquisitive feeding behaviour.

"Great whites usually feed on seals and other large pray like dolphins. They often investigate objects floating on the surface by biting it."

Ken Cashin The incident happened at Baylys Beach, near Dargaville, in Northland.

Trish Rolfe, who owns Baylys Beach Holiday Park, said the beach was popular with surfers and a number of them were in the water when the attack happened.

She said: "We just saw the fire brigade go past and then police, ambulance and then we saw the helicopter.

"It all happened very, very quickly."

Rolfe said shark sightings were not common at the beach, adding: "We've been here 11 and a half years and it's never happened before."

She added she didn't think the injured man was one of her guests.

Baylys Beach is a popular summer location close to the town of Dargaville.

Surf Life Saving New Zealand's website says the unpatrolled beach can be dangerous for swimmers and surfers due to strong rips, large holes and powerful waves.

​Police were at the scene around 7pm and said they would remain at the beach to provide advice to anyone in the area.