A Waikato Hospital spokeswoman confirmed three children, all aged under 10, and a woman in her 60s were brought to the hospital last night.
The woman was in a critical condition in the intensive care unit today.
Two of the children, both boys, also remained in hospital. One remained in a serious condition and the other was stable in a ward.
A third child, a girl, was discharged from hospital today.
Three other victims of the crash were taken by road to Taupō Hospital in a moderate condition. There were eight people travelling in the two vehicles.
The highway was closed for three hours last night while emergency services cleared the scene.
The crash comes just four days after a Waikato Hospital emergency department nurse posted on the hospital's Facebook page about the aftermath of road crashes and urging people to drive carefully.
Waikato District Health Board clinical nurse specialist Mike Haden-Jones said in the January 14 post that 382 people died on New Zealand roads last year, four more than in 2017 and the country's worst road toll in a decade.
"Our region had the highest number of deaths with 17 per cent of the fatalities occurring on Waikato's roads," he wrote.
The figures don't take into account the thousands of accident victims who didn't die but were instead left with life-altering injuries, Haden-Jones said.
"Like the police, and other emergency services, when I read articles about our road toll I don't see the figures - I see faces, I see families," he said.
"I remember number 44 out of 382 – a young man in his first car, losing control on a corner, his mother's face as she is told he didn't survive.
"Number 211 out of 382 – a young mother, her children without her this Christmas - these are real cases although the numbers are not accurate.
"I deal with the aftermath. I hear the stories from the scene. The same stories again and again and I watch that road toll ticking ever higher. I watch as people seem not to learn from recurring mistakes."
Hi everyone,
I try really hard to keep the content I put out light. No-one likes being preached to and ultimately, I...
Posted by Waikato Hospital on Sunday, 13 January 2019
It's why he wrote the post, Haden-Jones said.
"Because when I see those newspaper headlines it physically hurts. We are getting it badly wrong and as a nation of drivers we are failing."
He pointed to four factors in road crashes:
• Excessive speed, including not driving to the conditions;
• Failing to wear a seat-belt - a third of those who died were not restrained at the time of impact;
• Distraction either by other passengers or frequently from mobile phone use, and;
• Driver impairment due to fatigue, alcohol or other drugs.
"I sometimes wish I could take my camera into one of our resuscitation rooms after a trauma and show you the aftermath; I went as far as taking pictures once. Putting those pictures on Facebook would horrify many."
Haden-Jones said it was easy to "shake your head sadly and move on" from numbers in a headline.
"Trust me as someone who knows, it's a lot harder to put these things behind you when that number has a face, a name and a family."
Haden-Jones said his driving had changed as a result of his job.
"I'm very aware of my speed, my behaviour, and that of everyone around me. I guess that is all I can ask of you. At this time of year some of us are making resolutions for a new year, a new us.
"Please let's start 2019 with new driving habits. We can all make a difference."
