An 18-month-old baby has been savaged by the family pitbull, in one of the worst dog attacks seen by hospital emergency staff.

Research by a Middlemore Hospital emergency nurse has revealed 65 children were so seriously injured by dog bites in the past year that they were brought from around New Zealand to the hospital, which specialises in plastic surgery for serious facial injuries.

Donelle Whiu, a charge nurse and dog behaviourist, measured the injuries on the internationally recognised Dunbar Dog Bite Scale, on which level 1 indicates a minor injury and 6 a fatality.

Three children sustained level 5 bites - meaning the dog "bit to its full potential" repeatedly and as far as the teeth could sink into flesh.

These attacks were on:

* A 5-year-old girl who was bitten multiple times on the chest and back and dragged up the driveway by a neighbour's cross-breed dog.

* An 8-year-old boy who was bitten on the face, arm, chest and side by a pitbull while playing in a driveway. The dog had allegedly got in through an open gate.

* A 15-year-old boy who suffered "big tears" and needed hundreds of stitches after being stopped by a police dog after a robbery. Whiu said the German shepherd in this case "was just doing its job".

But she said the worst attack of all was in April this year, on an 18-month-old baby who suffered "the worst injuries I've seen in my 15 years working in the emergency department".

Incredibly, this case was only classified as a level 4 attack, along with 17 other attacks, because the dog just gave the baby "a warning bite".

Whiu said the 18-month-old was bitten by the family's pitbull to get the child away from its food. "It was just because of the boy's age and size that there was just so much damage," she said.

The four worst cases have never been made public before as there is no mandatory reporting of dog bites. As a result authorities have no idea of the full extent of the problem.

The statistic that gives the best insight is the 10,000 ACC claims made every year but dog researcher John Payne estimates the true number could be as high as 25,000 attacks because owners are unwilling to report their own menacing pets.

A source said the 18-month-old baby's injuries were so horrific that it looked as if the pitbull had tried to "eat" the child. The dog was the beloved family pet, which had never previously shown aggression.

Animal Management managing director Barry Gillingwater said the family brought what he believed was a pitbull-cross dog to one of his centres and signed it over for destruction, saying it had attacked their 18-month-old.

He said the family had been traumatised by their baby's injuries and devastated that their pet of many years could have done such harm.

"It was a very traumatic event," said Gillingwater. He urged every parent to be wary of the potential for a family dog to turn on children, because ultimately dogs were "pack animals" and any breed could bite.

Gillingwater's company provides dog-bite prevention talks in schools in Manukau, Franklin and Wellington, and he hoped in the future his talks could spread further to warn more children.

Dr Ashwin Chunilal, the plastic surgeon who worked on the baby, said that the family did not wish him to discuss the case and he respected this wish.

Whiu said the baby's case highlighted a finding from her research that 63 per cent of dogs that bit children were known to the family.

In one case in five the dog concerned was the family pet. Only 9 per cent of attacks were by strange animals.

She said: "People are more at risk at home than on the streets."