The Department of Conservation has been forced to issue a warning to visitors to national parks after staff found Aucklanders carrying pet cats up Mt Taranaki in backpacks.

The extraordinary alert was prompted by a bizarre feline incident but a spokesman said cats are not the only animals straying into some of our most pristine wilderness.

DoC senior ranger Dave Rogers said staff saw the cats, who were rugged up against the cold in their own little jackets, being loaded into backpacks in a car park at Egmont National Park.

"Cats and all other domestic animals are not allowed in the National Park as they pose a threat to endangered birds such as kiwi and whio, and other native species including geckos and insects," Rogers said.

When approached, the owners, who were visiting from Auckland, said they weren't aware of the rules, which prohibit pets in the National Park. Photo / DOC

"Bringing a pet into the park may seem a harmless thing to do," Rogers added, noting that dogs, rabbits and even a parrot have been brought into the park recently, "but it has potentially deadly consequences for our native wildlife, particularly should the pets run loose or escape from their owners' control."

He said the animals could have a devastating effect on the native wildlife in the area.

"Our conservation land is vitally important for the survival of endangered species. Many of our native birds are flightless and have few or no defences against predation. A dog can sniff out and kill a kiwi with ease. Uncontrolled dogs and cats can severely impact our native wildlife.

"Even the most docile and well-controlled pet can instinctively kill."

DoC advised that no pets are permitted in National Parks or dog prohibited areas unless express written approval is granted and those flouting the rules face an instant infringement fine of up to $800, with repeat offenders being liable for fines up to $100,000 or up to a year in prison.

Anyone seeing a domestic animal in the park can contact their local DOC office or phone the DOC hotline on 0800 DOC HOT (0800 362 468).