A 4-year-old boy was saved by his child seat and restraints when the car he was in and a full milk tanker collided on State Highway 1 near Palmerston.

The boy was extremely lucky to survive the crash yesterday with just a cut to his knee, Senior Constable Stefan Witehira said.

"The 4-year-old was in a child seat and restrained and I would, without a doubt, say that has saved him from serious injury or worse," he said.

The boy's 25-year-old father was next to him in the back seat of the car, which was driven by the man's 54-year-old mother. His 65-year-old father was the front seat passenger.


All were wearing seatbelts.

Mr Witehira said members of the public stopped to help the family after the 2pm crash, about 1km south of Palmerston in a 100km/h zone.

All but the 25-year-old man were out of the vehicle by the time emergency services arrived.

The young father had a non-life threatening head injury and was taken to Dunedin Hospital in the Otago Regional Rescue Helicopter.

His son and parents were taken to hospital by ambulance.

Mr Witehira said the driver had a sprained ankle and her husband was not injured.

The milk tanker driver was "shaken" but not injured.

It appeared the northbound vehicle crossed the centre line and hit the southbound milk tanker, he said.