A woman who had her cat badly savaged by a dog may be forced into homelessness to pay for the cat's vet bills.

Wellington woman Jan Walton's cat, Tom, was seriously injured with a broken pelvis and a potential broken leg on Monday morning.

The 10-year-old cat was stretched out enjoying the sunshine within the Camp Elsdon boundaries, where Walton lives.

Then a "large, muscular dog" was encouraged by its owners to attack the cat as it walked off the leash on the Colonial Knob in Porirua.

When the dog owners saw the cat they told the dog to "Sic 'em" repeatedly and continued to encourage the dog after he had caught the cat. It was only when a witness intervened that the dog dropped the cat.

Walton, who has been homeless for the past year and is dependant on a benefit, is trying to think of ways to pay for Tom's treatments. She said euthanising him was not an option.

"The SPCA said I was looking at an extreme amount of time and extreme money. I'll move out, live in my car and they can have my benefit each week to pay for the vet.

"I won't kill him. I wouldn't kill a 10-year-old child. I've had 10 years with this cat."

Walton said the attack was kind of ironic as she got Tom after he had been attacked by a dog when he was 3 weeks old.

Walton became homeless as the Porirua house she was living in was "soaking wet". Paramedics came to visit her for her severe asthma and a blockage in her lung and they told her she should not live there. So she moved into her car and slept under a bridge for a year.

"I just left the windows open and Tom popped in and out as he pleased. Where I roam, he roams too.

"He's just a beautiful black cat who thinks he's not a cat. He thinks he's one of us. He's a laid-back guy."

Her luck had changed two weeks ago when the people who own Camp Elsdon offered her a cabin at an affordable rate.

The attack was the dog owners' fault for encouraging the canine, Walton believed. She did not want the dog destroyed.

"I do not want the dog put to sleep for no reason. This is a command from the humans. It's a little soldier who did its job. The dog is not at fault, it's the owners."

Inspector Gina Kemp was called out to the camp after the incident.

"It is incredibly concerning that a dog is being actively encouraged to bait other animals. It is especially concerning that the attack was instigated unprovoked and with witnesses present.

"I am very concerned this will not be an isolated incident - or that this behaviour may escalate if the perpetrators are not found."

SPCA general manager Ros Alsford called the attack "horrific and totally unnecessary".

"It's sad they are encouraging their dogs to do that. People who have pets love their animals. It's not fair people are encouraging theirs to hurt another person's pet."

The SPCA had launched an investigation and information was already coming in, Alsford said.

The SPCA set up a Givealittle page for Tom the cat which you can donate to here.