Crash analyst Jeff Cramp, of the police Serious Crash Unit, said the vehicle had gone off a straight section of road into a drain and hit a driveway culvert.
There was no obvious cause or mechanical fault. The investigation was continuing.
Police, volunteer firefighters from the Kaitaia and Ahipara brigades, two St John Ambulances, the Northland Rescue Helicopter and a Westpac Helicopter from Auckland responded.
The crash closed Kaitaia-Awaroa Rd between the Roma Rd junction and north of Herekino, causing large queues.
Normal summer traffic in the area was compounded by more cars than usual using Kaitaia-Awaroa Rd, the main west coast route to Kaitaia while State Highway 1 is closed at Mangamuka Gorge.
Kaitaia traffic was diverted via Waiotehue Rd, an unsealed back road.