A New Zealand man has good reason to question whether his dog is truly his best friend after his family pet shot him in the backside in a potentially fatal accident.

The 40-year-old man was sitting in the back seat of his car when the dog stepped on the trigger of a loaded .22 rifle and shot him, police told the Northern Advocate newspaper on Wednesday.

The wounded man was with a group of friends who had just finished killing and butchering a domestic pig, and he thought the rifle had been unloaded.

He was rushed by helicopter to a nearby hospital in the far northern town of Dargaville where doctors said he underwent surgery to remove a bullet from his left buttock.

Dargaville police constable Ian Anderson said the man was lucky not to have been more seriously injured.

- AFP