"It definitely wasn't moving. It was dragging along like a wet blanket. It was gruesome."
He gave up the pursuit when they reached Kerikeri, as he didn't want to confront the driver and create a scene. And by that stage the dog was dead."
He believed the dog, which appeared to be a huntaway, may have been dead when he first saw it.
"The driver had tied the dog on a rope on the right corner of the ute rather than the middle, where it couldn't leap off. If you're going to have a dog, be responsible and tie it up in a sensible spot," he added.
Two other hunting-type dogs were on the back of the vehicle, but he couldn't see if they were secured. He took the car registration and reported the incident to police, while another resident reported it to the SPCA.
An SPCA spokeswoman said the incident was being investigated, and confirmed that the dog was dead.
Animal welfare code regulations introduced in 2018 require that dogs be secured in a cage or crate, or tied up safely when travelling on the back of vehicles on public roads. If a rope is used it must allow the dog to stand and lie down in a natural position and prevent it from getting its legs over the side of the vehicle.
The only exception is farm dogs, which can be loose on a vehicle when they are actively working.
Breaching the regulations carries a fine of $300.
Animal advocate Leonie Exel, from the Bay of Islands Watchdog, said the driver "may have just made a terrible error," and urged people not to rush to judgment.
"Some people aren't aware of the changes in legislation and what it is they need to do. If your dog is on the back keep a close eye on it, or better still put it in the cab," she said.