Two conservation dogs are being sent to Rangitoto and Motutapu islands after reports of a cat sighted on the predator-free land.
The Department of Conservation said they are taking two possible sightings of a black cat, at Islington Bay, which connects the two islands in the Hauraki Gulf, "very seriously".
Rangitoto and neighbouring Motutapu have been free of cats, rats, possums, mice and other animal predators and pests since 2011.
The cat sighting poses treat to native birds, bats, lizards, wētā and other native insects.
Birds such as the endangered tieke, or saddleback, tui and kaka call Rangitoto home.
"We need to know if there is, or isn't, a cat on Rangitoto or Motutapu in the Islington Bay area. So we've launched a response to determine if there is a cat there," said acting DOC Auckland Inner Islands operations manager John Galilee.
"We're sending two conservation dogs, trained to detect cats, and their handler, to Islington Bay to try and establish if there's a cat in the area."
The conservation dogs and their handler are due to arrive at Islington Bay on Thursday morning.
Motion-sensitive cameras, cat tracking devices and traps designed to catch cats are also being placed in the area of the sightings.
The traps have been approved by the National Animal Welfare Advisory Committee.
"We have biosecurity systems in place because there's an ever-present risk of a cat, rat or mouse making it to one of these islands," Galilee said.
"We want to remind the public that cats and dogs are not allowed on pest-free islands.
"That's because of the serious threat they pose to native birds and other native wildlife on these islands."