Police are appealing for the public's help to find a tan-coloured short-haired pitbull terrier dog that attacked and killed another dog in Tairāwhiti on Sunday morning.

Ruby, an 11-year-old cavalier King Charles spaniel, was being walked by her owners near the corner of Frances Street and Moana Road in Okitu at 8:35am when the attack occurred.

Detective Senior Sergeant Mark Moorhouse said the person with the pitbull terrier was a woman between 40 and 50-years-old, wearing black sunglasses, a grey hoodie sweater and black pants, and of Maori or Pasifika descent.

A passing police unit intervened when they saw the attack, using pepper spray to separate the pitbull terrier from Ruby.

"However Ruby suffered horrific injuries and died before help could arrive."

Det Snr Sgt Moorhouse said the woman spoke briefly to police staff at the scene, but despite being asked to wait with the offending dog she left while police were trying to help Ruby and her distraught owners.

Police are now appealing to the public for any information, including video footage that may assist them with identifying the dog and its owner.

"We are concerned that this could happen again so it is important the dog is identified as soon as possible."