A Purerua woman who watched as four men prepared to detonate some sort of explosive device on the beach at Rangihoua Bay, on the Purerua Peninsula, on Saturday night, and saw the flames spread into bush in Rangihoua Heritage Park, said the most upsetting thing was hearing kiwi "screaming" as the hillside burned.

"We're familiar with the bay and the sound of kiwi calling. Those were definitely distress calls," Vanessa Owen said.

Some witnesses believed the explosion was caused by a petrol bomb, others that the device was made from a large quantity of fireworks. Firefighters described it as a home-made incendiary device.

Mrs Owen and her husband Richard were on their moored boat about 200m offshore when they noticed something unusual on the beach. At first Mrs Owen, who kept watch with binoculars, thought the four men were digging a hole in the sand for a beach barbecue, and were acting surreptitiously because of the fire restrictions.

Advertisement

Three of them then retreated to Marsden Cross, the monument marking the site of New Zealand's first church service in 1814, while the fourth walked slowly backwards along the beach, away from the hole. At first she thought he was preparing a long line, but she now believes he was laying out a trail of petrol.

"Then it just exploded. The flames bounced into the bush," she said.

A Salt Air helicopter and a Rural Fire appliance at the scene the following morning. Marsden Cross is on the right. Photo / supplied
A Salt Air helicopter and a Rural Fire appliance at the scene the following morning. Marsden Cross is on the right. Photo / supplied

She phoned a friend who lived nearby as the flames raced up the bank, while her husband called 111. With the Kerikeri police station 40 minutes away, she called a friend and asked him to intercept the men at the car park.

Two of the men had driven away by the time her friend arrived, but the others had just made it up the hill. St John and a doctor who lived nearby were called when one of the pair appeared to suffer a seizure.

Mrs Owen said it had been impossible to identify the men through her binoculars — all four had baseball caps pulled down over their faces — but she had no doubt that at least one of them was a Pākehā given the whiteness of his buttocks when he 'mooned' her.

Deputy principal rural fire officer Michael Champtaloup said seven fire appliances and about 30 firefighters from Kerikeri, Kaeo, Kaikohe, Kawakawa and Ōkaihau responded.

There was no road access, but four-wheel-drive trucks from Kaikohe-based Rural Fire were able to get down to the beach and pump sea water to douse the flames.

A Salt Air chopper from Paihia spent about two hours on Sunday using a monsoon bucket to put out hot spots on a cliffside too dangerous to access from the ground.

Advertisement

Mr Champtaloup described the cause of the fire, which covered about 1ha of ground on the side of Rangihoua pā, as "some sort of home-made incendiary device."

Police declined to comment while the investigation was continuing, but confirmed that some sort of device was involved.