A 10-year-old boy is in a critical condition in Wellington Hospital, after being flown there following a serious crash on State Highway One at Marycrest, just south of Te Horo.

It happened about 11.15 this morning.

Detective Slade Sturmey of the Horowhenua police says a white car northbound was stopped on the highway indicating a right turn into a driveway.

He says it was pulled as far right as possible in the northbound lane to allow vehicles to pass on its left.

He says a small truck failed to notice the car had stopped and collided with its rear, pushing the car into the southbound lane where it collided with another white car.

There were two adults and three children in the right-turning car and all were taken to hospital.

A 10-year-old boy was taken to Wellington by Westpac Rescue Helicopter in critical condition and is undergoing surgery.

A seven-year-old girl has spinal injuries and injuries to her and the others are not life threatening.

The two occupants of the truck were treated at the scene and required no further treatment.

Detective Sturmey says there were two adult passengers in the white southbound car and three people were treated at the scene and did not require further treatment.

He says initial indications are that alcohol was not involved, but says that cannot be ruled out.