A man who helped drag people from mangled wrecks in the fatal Taupo car crash has described seeing "the worst possible nightmare" unfolding in front of him.

Called one of the worst crashes police have seen in 20 years, the deadly two-car smash north of Taupo on Tuesday afternoon killed four people, including a 5-year-old boy, and injured eight more.

The first of the dead to be named was Pesi Tuivai, a mother and newly ordained lay preacher, whose 10-month-old daughter is fighting for her life in Starship Hospital.

Melbourne-based Kiwi Peter, who asked not to use his last name, was one of the first to reach the mangled wrecks.

Peter was heading back to Auckland on State Highway 1 when the crash unfolded in front of him.

"It was like the worst possible nightmare," he said.

Peter pulled over and was the first to reach the mangled wrecks. There was petrol everywhere, he said.

The little people-mover was silent.

"There was no sign of life."

From the other vehicle he heard wailing and screaming.

"My first thought was 'we have to get them out before there's a fire'."

He and other bystanders at the scene rushed to the larger vehicle and focused on getting people out.

"I carried the mother out of the front passenger seat with the help of two other people," Peter said.

He couldn't say how many people were pulled from the wreckage, but recalled seeing two babies in car seats.

They got everyone out except the male driver, who was alive but pinned against the steering console, Peter said.

"He was not in a good way. We decided to wait for emergency services to arrive."

Then someone noticed the baby in a car seat in the other car, alive.

They managed to pull the baby from the wreck, holding and comforting survivors as they waited for emergency services to arrive.

It was 15 or so minutes but it "seemed like forever", Peter said.

The baby was quickly flown to Starship Hospital in Auckland, where she remained in a critical but stable condition last night, police confirmed.

Her mother, Pesi Tuivai was the first of the crash victims to be named.

Tuivai was supposed to have given her first sermon as an ordained lay preacher in a few weeks.

Instead, her family is facing the terrible task of preparing for her funeral.

Free Wesleyan Church of Tonga minister Tevita Langi told the Herald yesterday Tuivai was returning to Palmerston North after travelling to Auckland to be officially sanctioned to speak from the pulpit.

Heartbroken relatives, including two of the dead woman's sons, gathered at Langi's home last night to pray. Others in the Polynesian congregation gathered in Palmerston North to mourn the loss of the cherished parishioner and pray for those in hospital.

Langi described Tuivai as a warm-hearted woman who doted on her children.

"She was a kind, loving mother.

"Every time you met her she would have a big smile on her face."

Tuivai's husband, coping with the tragic loss of his wife, was in Auckland at the bedside of his badly injured girl.

"I spoke to him last night. He's devastated."

Langi said everyone inside the crashed car were related to each other.

The crash also killed a 5-year-old boy, a 56-year-old woman and 60-year-old man, travelling with a fourth person in a five-seater northbound van.

Police said the horrific crash was "absolutely devastating" and were now piecing together why the vehicles collided head-on.

Seven other people were taken to hospital, including two girls, aged 2 and 3 years, who were being treated for minor injuries at Rotorua Hospital.

A 42-year-old man was in the Intensive Care Unit at Waikato Hospital and a 66-year-old woman and 17-year-old girl were in Rotorua Hospital, all in a critical condition.

A 32-year-old woman was stable in a ward at Hamilton Hospital.

A fifth woman, 42, was taken to Rotorua Hospital but not admitted.