The mother of the children involved in the truck crash on the Napier-Taupō Highway overnight has thanked emergency services and motorists who stopped to help at the time of the crash.

Three children and an adult were injured after the truck they were in left Napier-Taupo Rd and slammed into a power pole causing a large scrub fire, just before midnight last night.

An injured grandfather tried desperately to pull his young granddaughter from a crushed truck cab - her legs trapped by a toppled power pole - as a scrub fire fanned to life within metres of the wreckage.

After the crash, passing motorists and truckies heroically pulled the driver and two young school-age children from the mangled truck.

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"We want to thank everyone who helped free dad and the children, and get them out of the truck - they did a wonderful job and we are very grateful," the children's mother said.

Two of the children aged seven and five along with the children's grandfather had been discharged from Taupō Hospital.

An eight-year-old girl remained in Hawke's Bay Hospital in a stable condition and was recovering well.

The family also wanted to thank Taupō and Hawke's Bay Hospitals for the care the children and their grandfather received.

Downed lines sparked a large scrub fire that quickly spread to a 100m fire front and burned out of control along the highway hillside throughout the night.

Rural fire crews and helicopters with monsoon buckets were still battling the blaze this morning.

Taupo Fire Brigade acting station officer Sean McAvinue said Taupo fire crews received the call at 12am and immediately set for the scene 50 minutes away expecting the worst.

"We knew there was a truck that crashed into a power pole which started a large fire and people were trapped."

By the time emergency services arrived at the remote stretch of central North Island highway passing truckies and bystanders had managed to pull the driver and two children from the crumpled cab in the pitch dark - but an 8-year-old girl remained pinned inside, her legs wedged tightly beneath the dash by the roof collapsed under the weight of the pole.

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All the while flames threatened, coming within 5m of the frozen meat truck which had been heading to Taupo.

McAvinue said the girl's legs were so tightly hemmed in specialist rescue equipment was needed to free her.

"It was quite tricky to get her out because we were operating in the blind," said McAvinue.

Firefighters finally managed to get the roof off and remove her from the cab.

Power in the area had also been turned off to make the scene safe.

Fire crews from Napier, Taupo and rural areas, St John, police and the Lowe Corporation Rescue Helictoper attended the scene.

Rural fire crews contained the blaze then called off their efforts until daylight as it was getting too dangerous but continued to monitor the fire overnight, McAvinue said.

There were no houses or properties in range of the fire.

One child was flown by helicopter to Hawke's Bay Hospital. Two children and an adult were taken to Taupo Hospital.

St John Ambulance said one person suffered moderate injuries and three had minor injuries.

The Lowe Corporation Rescue Helicopter said an 8-year-old girl was flown to Hawke's Bay Hospital suffering minor leg injuries.

A Hawke's Bay Hospital spokesperson said the eight-year-old girl was in stable condition and Taupo Hospital confirmed the three other patients had been treated and discharged.

Traffic was able to move slowly past the crash this morning.

Police said the truck had since been removed.