A Hato Hone St John spokesperson said they were notified of the motor vehicle incident at 4.20pm and two ambulances, a rapid response unit and a rescue helicopter attended.
"We assessed and treated one patient with critical injuries who was flown to Waikato Hospital," the spokesperson said.
A Fire and Emergency NZ spokesperson said four fire crews responded to the two-vehicle crash and were at the scene for about half an hour.
A crash alert from Waka Kotahi NZ Transport Agency said that State Highway 29 was closed between Te Poi (SH28) and Tauriko, Tauranga (SH36).
"This section of SH29 is likely to remain closed for some time this evening as police undertake a serious crash investigation."
Motorists were asked to delay their journey or allow extra time for a detour to the south via SH28, SH5 and SH36 via Rotorua.
Alternatively, traffic travelling to and from Auckland should use SH2 via Karangahake Gorge.
Note: An earlier version of this article stated that the woman flown to hospital suffering critical injuries had died. This was incorrect. A 19-year-old man involved in the accident died. The error is regretted.
