One photograph showed the woman's right arm, from the elbow down, had been eaten through, exposing both bones and leaving a gaping wound about 15cm to 20cm long and between 5cm and 8cm wide. All of the flesh had been removed from the lower arm and there were some large bite wounds on her upper arm and biceps.
It was not clear if the woman broke her leg before or after the attack.
Mr Coutts said the dog was understood to be owned by the woman's grandson and she had asked for it to be left with her for company.
Mr Coutts said the injuries were "massive, the worst I have ever seen. She must be one tough lady because I can't see how she has survived."
He said he doubted if he would see anything worse in his career and she was lucky the dog did not sever any major arteries.
"I'm amazed, normally someone would have died of shock ... but they tell me they may be able to save her arm."
Mr Coutts said the owner of the dog had surrendered it to Animal Control officers and it would be put down.
"This dog was not previously known to us, it was registered, it was microchipped and the owner, from what I can gather, appeared responsible."
However, he said, the dog was not desexed.
He said american pitbulls or pitbull-crosses were highly unpredictable.
"Society has got to think seriously whether we want these types of dogs around, they are capable of doing horrendous damage - this was not a short, frenzied attack. People say they can trust these dogs with their children, but I never would."
Detective Senior Sergeant Zane Smith said Rotorua police were looking into the circumstances of the attack. He
could not say if charges were likely.
It is the fourth attack this year by an american pitbull or pitbull-cross in Rotorua.
On January 22, a 9-year-old Rotorua girl was bitten by a pitbull while walking in Puketawhero Park. She suffered cuts to her right arm and a wound to the right side of her head which required 20 stitches.
On January 23, a Rotorua man was bitten on the hand by a pitbull while walking along Miller St. The wound needed four stitches.
On Sunday, July 1, a 7-year-old Rotorua boy was seriously injured after his neighbour's dog attacked him, tearing a chunk of flesh from his leg.
The latest attack comes as the district council gets set to deliberate on its Dog Control Bylaw and Policy at a meeting scheduled for August 7.
Councillors were told by Mr Coutts at a recent council hearing on dog control that pitbulls and pitbull-crosses were responsible for a disproportionately higher number of attacks on people than any other type or breed of dog.
