A young woman was heading home to Tauranga after visiting family in Cambridge when she died in a crash in the Waikato overnight.

The woman in her 20s was the passenger in a Nissan Skyline when it and a people-mover crashed head-on on State Highway 1, near Hydro Rd, at Karapiro on Saturday night.

A Tauranga woman was killed and several others were injured in a head on crash on SH1 near Karapiro. Photo: Waikato Westpac Rescue Helicopter.

It's understood the woman, and man in his 20s who was driving the car, were returning to Tauranga after visiting the woman's mother when the crash happened on a straight section of road.

The fatal crash was one of six collisions in three hours in the Waikato district on Saturday evening.

Waikato Serious Crash unit is continuing to investigate the crash but said initial indications showed two vehicles, each with two occupants, collided head-on.

The woman - a passenger in the southbound-travelling sedan - remained trapped in the vehicle and died at the scene.

Another woman in her 30s, who is five months pregnant, suffered a fractured sternum and was airlifted to Waikato Hospital by the Waikato Westpac Rescue helicopter in a serious condition.

She was a passenger in the people-mover heading north when it crashed with the Nissan. Police say several others were taken to hospital by road - two in a serious condition and one in a moderate condition, says a Waikato Hospital spokesperson.

Initial reports also listed a child in moderate condition but this could not be confirmed.

When emergency services arrived at the scene, Cambridge fire chief Don Gerrand says the woman was trapped in the passenger side of the Nissan.

She was being helped by at least one doctor who came across the crash while travelling in a car behind, he says.

"The road was jammed up and there were several medical people already on scene - a couple of doctors who were passing motorists were mainly working on the woman."

He says the young man with her was already out of the car. Her mother from Cambridge arrived shortly after.

"We were there for probably an hour and a half."

The fatal crash was the first of several others in the Waikato at the weekend.

At 7.30pm on Saturday, a vehicle using the diversion in place for the Karapiro incident crashed into a powerpole on Whitehall Rd.

The driver had left the scene in another vehicle before police arrived.

An hour later, there were two further crashes - one in Matamata where there were no injuries reported, and one in Huntly, where there were minor injuries reported.

"While not as serious as the Karapiro crash, all crashes have the potential to cause devastation to families," police said in a statement.

And in Taupiri, police attended a three-vehicle crash on State Highway 1. There were no reports of injuries.

The crashes came less than 24 hours after another serious crash on SH1 not far from Karapiro at the SH29 intersection.

Two vehicles again collided head-on on the highway at 6.30pm Friday.

One man driving one of the vehicles was in moderate condition with lower leg injuries, the Waikato Westpac Rescue helicopter service said in a release.

A woman driving the other car was trapped in the vehicle and was freed by firefighters. She suffered abdominal injuries and was flown to Waikato Hospital in a serious condition.

"As the festive season approaches everyone using the roads need to ensure they are safe drivers, road safety is no accident, and we want to make sure that all of the family is around the table to celebrate Christmas."