A baby critically injured in a crash near Kopaki, Waikato, this morning was unrestrained on its mother's lap when the car hit a bank.
District Road Policing Manager Inspector Freda Grace said the car crossed the centre line a crashed in to a bank on the other side of the road about 8:30am.
Four adults, a three-year-old and a baby aged under one were in the car.
Unrestrained, the baby has been thrown into the rear interior of the car and suffered critical injuries.
A helicopter was called to airlift the baby to Auckland's Starship Hospital but this was delayed for quite some time due to poor weather conditions.
''The baby was taken to Te Kuiti hospital and then transferred by helicopter to Starship. A three-year-old sibling and the children's' mother were taken to Waikato Hospital by ambulance with minor to moderate injuries while three other adults were treated at the scene,'' Mrs Grace said.
Mrs Grace said crash investigators are working on establishing what, if any, part two bald tyres on the front of the car played in the driver losing control on the downhill stretch of road.
"It may be that the speed was too fast for the conditions and the condition of the tyres contributed to what happened.
"From a police perspective, we want vehicle owners to ensure their vehicles are roadworthy at all times, not just at the one point in time when their warrant or certificate of fitness is issued. At the same time we want them and their passengers to be fit for the road too, meaning they are alert and properly restrained."