State Highway 1 has been reopened after three vehicles, including a petrol tanker, crashed at Ohakuri this morning.
The petrol tanker driver is in a serious condition and was flown to Waikato Hospital.
St John confirmed it sent two ambulances to the crash following the emergency call at 7.40am.
Just before 9am, Fire and Emergency New Zealand northern shift manager Paul Radden said the driver of the tanker was trapped but crews had "extricated him".
The highway was closed for a time between Thorpe Rd and Chestnut Rd, south of Atiamuri between Taupō and Tokoroa, but has since reopened with traffic management, according to the New Zealand Transport Agency Facebook page.
The latest post said traffic was being managed with a stop/go sign, and a detour was no longer required.
"Please allow extra time for delays in both directions until the scene can be fully cleared."
A police spokeswoman said the tanker was leaking at the time of the crash.