A New Zealand man who cooked his pet dog in a backyard pit cannot be prosecuted, because it was killed humanely.

The Society for the Prevention of Cruelty to Animals says inspectors arrived at the South Auckland home to find the pitbull terrier-cross skinned, gutted, and partially charred.

The puzzled owner, Paea Taufa, says dog is a delicacy in Tonga and he had knocked it unconscious with a blow to the head before slitting its throat.

The SPCA says cultural differences aside, it is unacceptable.

But killing a dog is not illegal in New Zealand if the animal is slaughtered swiftly and painlessly.

- AAP