LATEST: A school holiday road smash involving a car full of kids near Mt Ruapehu has left two people with serious injuries at Waikato Hospital.

The crash between two vehicles occurred on an 80km/h stretch near the intersection of State Highway 4 and 47 at National Park around 10.55am.

A National Park Backpackers staff member, who didn't want to be named, said the silver car was travelling north along SH4 when a small green Holden emerged from a side road.

He understood the green car had three passengers, possibly a mother and two children, while the silver car carried a mother and six children from Palmerston North who were heading to Kawhia for a holiday.

''[The driver of the silver car] tried to avoid them,'' he said.

''She was pushed off the road onto a bank and the other car was spun around and just sitting in the road.

''There were little kids in the car so she was really lucky.''

He said the green car didn't flip but it was badly dented and firefighters used the jaws of life to cut the occupants free.

Police central communications team leader Chris Turner said one person received serious injuries and another moderate-to-serious injuries.

The Waikato Air Ambulance and the Taranaki Rescue Helicopter both attended, alongside ambulance staff, and transported one patient each to Waikato Hospital.

The backpacker's staff member said he transported the mother and her six children back to Palmerston North via bus at 1.30pm.

They were shaken but unhurt, he said.

- © Fairfax NZ News