A St John spokeswoman said a teenager also received moderate injuries to his hand and was taken to Bay of Islands Hospital.
The driver of the Toyota and his remaining passenger, along with the driver of the Nissan, were treated for minor injuries at the scene.
"There is clear evidence that the wearing of seatbelts lessens the risk of injury in a rollover crash such as this," said acting Sergeant Julian Trinder.
"We implore everyone to take the time to ensure that their seatbelt is correctly fastened, before they start their journey, so that they can reach their destination safely."
Northern fire service spokeswoman Megan Ruru said three people were outside the vehicles when fire crews arrived and another five people were in one car.
Police set up a cordon at Wehirua Rd last night.
Police have not ruled out the possibility of charges being laid.
The Serious Crash Unit is investigating to establish the cause of the accident.
Northland Police would also like to hear from anyone who may have witnessed the crash or who may have come across it shortly after it happened.