Emergency services were called to the scene of the two-car collision in June.

A newborn baby girl is among seven people killed in a "devastating" car crash in Taranaki, and police say it's possible one other critically injured may yet die.

Two cars collided head on, killing four elderly people in one car instantly, as well as a man and the baby in the other vehicle.

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GRANT MATTHEW/STUFF Police have held a debrief for emergency services staff who attended the scene of a car crash that claimed seven lives just north of Waverley on June 27. (file photo)

The survivor, a woman and an eight-year-old girl, have been taken to separate hospitals in a critical condition.

The crash - one of the worst local fire crews said they had ever seen - happened on State Highway 3 near Waverley on Wednesday.

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Inspector Dave White, central district road policing manager, said the crash was "an absolute tragedy"..

"Dealing with a crash like this today is just devastating," he said. "There's no other words for it, really."

Police would not comment on the cause of the crash, but warnings had been issued earlier in the day about icy roads in the area following four other crashes in two hours.

Kris Boult/Stuff The crash happened shortly after 7pm.

At the time of the crash, the temperature at the Taranaki Regional Council's closest monitoring site in Patea was 10 degrees Celsius. Tuesday night was one of the coldest the region has had this year and the Patea site dropped as low as 1.8C at 7.40am on Wednesday.

However, the sky was clear across the whole region on Wednesday and there had been no rain overnight Tuesday.

Harry Wilson, NZTA director of safety and environment, said they were "deeply saddened" by the fatal crash.

"The Serious Crash Unit is investigating and we will receive their report once completed," he said.

"As is the case with all fatal crashes on the state highway system, we will also carry out our own review of the road and roadsides, from a safe system perspective."

Chief fire officer for the Pātea fire brigade, Grant Hurley, said it was one of the worst crashes he'd been to.

"It was a bit of a mess, a bit of chaos," he said.

"One vehicle, they were all deceased; there was a baby involved in the other car that was also deceased."

He wasn't sure whether the first responders had pulled the child free or if she had been thrown from the vehicle.

Kris Boult/Stuff Three helicopters were called to the scene of the late-morning crash in south Taranaki which killed seven people.

HOW IT HAPPENED

The crash happened on Wednesday morning, about 300 metres north of the intersection of SH3 and Ihupuku Rd, just outside of Waverley.

Police said it was a head-on collision on a corner governed by an 85kmh speed indication sign.

GRANT MATTHEW/STUFF Emergency services work at the crash scene, just north of the Taranaki town of Waverley on June 27. (file photo)

The woman in the same car as the baby was taken to Wellington hospital and the eight-year-old to Waikato hospital in Hamilton. The girl died early on Thursday morning.

Wellington Hospital said the woman remained in the intensive care unit on Thursday morning, and was in a serious condition.

Emergency services from the town, as well as Pātea and Whanganui, were called to the crash just after 11am.

Five people were initially reported dead by police and several others critically injured. A sixth person died at the scene about 2pm.

The Serious Crash Unit was at the scene and could be seen scouring the grass verge around the area.

One car was covered in what looked to be tarpaulin, while the other had its doors and centre pillar from one side fully cut out. The roof was still on but there was a big hole in the middle of the car.

'NOT SURPRISED'

A Waverley local, who didn't want to be named, said a signpost near the crash site had been damaged recently and not replaced.

"I think the arrow blew off in one of the last storms and was never replaced ... I do 45,000km a year across New Zealand and that corner drags you over if you don't know it well and I'm not at all surprised to see a massive fatality."

A woman at the Clarendon Hotel in Waverley said she'd never had any trouble with the stretch of road where the crash occurred, but said it had been very icy on the roads in the area.

Mary-Lousie Healey, who works at the Waverley Four Square, said she had heard that there had been a head-on crash, the road was blocked "and it's quite serious".

Healey said ambulances and police had been flying past the Four Square for a while. She said when the crash first happened farmers were directing traffic.

SH3 had reopened, following emergency services' work at the scene.

ONE OF OUR WORST CRASHES

The crash is just the ninth with five or more fatalities since the turn of the century and the worst since five kiwifruit packers were killed when their car was hit by a logging truck near Katikati in the Bay of Plenty.

The worst crash of recent times was in May 2005, when nine people were killed near Morrinsville when a tourist bus crossed the centreline and collided with a Freight Lines truck.

The worst road smash in New Zealand was in Northland in February, 1963, when a bus carrying 35 passengers home from seeing the Queen at Waitangi crashed over a 30m slope, killing 15.