Chinese crested powderpuff Bolt was on a lead along Waiake Beach, North Shore on Friday morning when he was attacked by another dog. A pitbull bounded down the beach around 10am and set upon Bolt, "ripping his back open," Bolt’s owner said.

A morning walk on a North Shore beach turned to horror when a woman and her dog were mauled by a large pitbull-type dog.

The Torbay residents said they were angry a man had brought the pitbull to the beach, then left it unattended while he went swimming on Friday morning.

The pitbull bounded down Waiake Beach on Auckland's North Shore around 10am and set upon Chinese crested powderpuff Bolt, "ripping his back open," said the woman's husband. Neither of them want to be named for fear of retaliation by the pitbull owner after they called Animal Management and had the dog impounded.

JASON DORDAY/STUFF Chinese crested powderpuff Bolt was on a lead along Waiake Beach when he was attacked by a pitbull.

When his wife tried to protect their pet the pitbull lunged at her, biting her hand.

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The man said he heard Bolt "yelp" followed by screams.

Beachgoers rushed to their aid but the pitbull had latched onto Bolt. One man kicked at the pitbull, they said. Eventually the owner appeared and managed to control the pitbull.

"It would have killed [Bolt], he's a tiny little thing."

Both were shaken: Bolt required clips in his back to fix the wound and his wife took the day off from work as a nurse in a rest home, he said.

Dog control responded and spoke with the person who had brought the pitbull to the beach. He was not the registered owner.

He claimed he had bought the dog only a week ago.

The pitbull was taken to the pound and would be released if the registered owner came to collect it.

Auckland Council guidelines allow dogs to be off-leash at Waiake Beach between 5pm and 10am between Labour weekend (September) and March 1.

However, there were no signs at the beach enforcing this, the man said.

"We've been left with vet bills, ambulance bills... but I'm really concerned this dog will just be free to do whatever it wants".

"We will never ever visit that beach again," he said.

A police spokeswoman said they responded to the incident around 10.20am, alongside St John Ambulance crews.

Auckland Council had been notified, she said.