The crash site is between Turrells and Kaituna Valley Rds intersection with State Highway 75 near Prices Valley.
Motorists have been advised to avoid the area, said a police spokesperson, as no diversions are in place.
The Serious Crash Unit has been called and inquiries into the crash are ongoing.
The highway was recently reduced to an 80km/h speed limit given the history of crashes on the road.
Christchurch-Akaroa Rd has been the scene of numerous crashes over the years - last year a car rolled 50m down a steep bank after coming off the rural road.
The seriously injured driver crawled to the top of the bank where he was found by people driving past.