A four-year-old child is fighting for his life after a major crash north-west of Auckland.

The crash happened on Stage Highway 16 near the Coatesville-Riverhead Highway intersection shortly before 5pm.

Police say a car with three children in the back appears to have pulled out of a driveway, and collided with an oncoming car.

The four-year-old is in a critical condition in Starship Hospital with life-threatening injures.

Two other children are in a serious condition in Starship, and their parents are in North Shore Hospital in an unknown condition.

The driver of the other vehicle was not injured.