Police arrived at the crash scene at 5.40pm this evening near the Tarawera cafe.
The truck appears to have jack-knifed and crashed, blocking both lanes.
The driver of the truck suffered a medical event and is now in a serious condition in hospital.
The road will be closed for at least five hours, as there is a large diesel spill across the road which will need to be cleared.
Police are also waiting for a heavy haulage crane to right the truck and trailer before moving it off the road.
Motorists are asked to avoid the area until further notice.
ENDS
Issued by Police Media Centre