A four-year-old Californian boy had a wild ride but escaped serious injury after he drove off alone in his mother's car during rush hour, eventually rolling the vehicle over and crashing.

Police sergeant Andrew Goodrich said the boy's mother parked the car about 4pm yesterday to a use a nearby phone. The boy got out of his car seat and climbed into the driver's seat, put the car in gear and drove on to a busy city street.

Sgt Goodrich said the boy sideswiped a vehicle, then veered into oncoming traffic. At that point the vehicle rolled over once but landed back on its tyres and kept going, eventually crashing into some trees.

The officer told the Orange County Register the boy was taken to a hospital with what were believed to be minor injuries.

The Los Angeles Times reports that in all, the boy travelled about a third of a mile.