Police are urging motorists to take care, no matter how confident they are in their own driving skills, after a "shocking day" on the country's roads.
Two people were killed and one left in a critical condition after a crash between a car and a truck south of Waiouru on Tuesday morning. Both of those who died were in the car.
And two others died in a crash between a bus and a truck on State Highway 1 near Marton.
Whanganui Area Commander Inspector Neil Forlong called it a "chilling reminder of what can go wrong on our roads".
"In both cases, the vehicles collided head on, causing significant damage that created its own challenges for emergency services, who have had to use specialist tools to get into the vehicles.
"The focus of police is now on answering the 'how' and 'why' - determining what went so wrong."
Over the past few years, New Zealand has experienced on average about one death a day on the roads.
Forlong called Tuesday's carnage in the lower North Island a "worst-case scenario".
"This shows how little time you have to react to something going wrong. You might be a confident driver, but don't lose sight of the fact you're sharing the road with other people…
"We know this will impact a lot of people - family, friends, emergency service personnel, and the other motorists who were just on their way to a destination but stopped to help.
"If you're on the road, please take your time, and don't forget how quickly things can go horribly wrong."
He praised emergency responders "faced with something nobody should ever have to confront", and said support was being provided to the victims' next of kin.
So far there had been 208 deaths on the road, Ministry of Transport figures showed, fewer than at the same point of recent years.
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