According to police, the two people who died were travelling in the car. The critically injured young person was also travelling in the same car and was ejected from the vehicle in the collision.
The truck driver was unharmed but understandably shaken, police said.
The Serious Crash Unit has carried out a scene examination and the Commercial Vehicle Safety Team will assist the investigation.
State Highway 1 reopened this afternoon, initially one lane only, under traffic management.
Two dead in Marton crash
Police also confirmed that two people died after a bus and a truck collided on State Highway 1 near Marton.
Emergency services were called to the scene, under a rail bridge between Wings Line and Calico Line, at around 8:50am.
The two drivers were the only occupants of both vehicles.
Inquiries to establish the cause of the crash will likely take some time, police said.
Crash scenes ‘horrific’
Whanganui Area Commander Inspector Neil Forlong said both crash scenes were “horrific”.
“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,” he said in a statement.
“Today was a worst-case scenario.
“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.”
Support is being provided to the next of kin, and the members of the public who were first on scene.
“They were faced with something nobody should ever have to confront – but seeing people in need, they did what they could to help.”
Forlong urged anyone on the roads to remember the four lives lost - especially over the upcoming Labour Weekend.
“This shows how little time you have to react to something going wrong,” he warned.
“If you’re on the road, please take your time, and don’t forget how quickly things can go horribly wrong.”
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Eva de Jong is a reporter for the Whanganui Chronicle covering health stories and general news. She began as a reporter in 2023.