Senior Sergeant Glenn Saunders said the injured woman, aged 36, was a passenger and was thrown from the car in the crash, he said.
A police spokeswoman later confirmed there were seven people in the five-seater car when it crashed. The other six people escaped with minor or no injuries.
The police Serious Crash Unit was investigating. Early indications were that speed was a major factor.
Ngongotaha fire station officer Lance Taylor said two other people were injured and treated at the scene.
He said no-one was trapped in the vehicle when the fire service arrived.
Crews had attended from Tauranga, Greerton and Rotorua, as well as an operational support crew.
A reporter at the scene said a cordon had been established at the intersection with SH36 but traffic was still flowing on SH36. Traffic was being stopped from entering Te Matai Rd.