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.