The Westpac Rescue Helicopter airlifted the girl to Auckland's Starship Hospital, where she remains in the intensive care unit.
Two other people were taken to hospital by ambulance.
A St John Ambulance spokeswoman had earlier said that two people were in critical condition and two others were in a serious condition.
Police said one of the survivors had life-threatening injuries.
Two ambulances and one helicopter were called to the scene.
Pouto Rd was closed following the crash.
A resident, who did not want to be named, said they could see the crash site from their home.
"There was a lot of activity down there with helicopters and emergency services," the neighbour said.
"We're a very tight community and it's quite rare for an accident to happen round here. It's just tragic."
