A critically injured person is being cut from a vehicle after a car and truck collided on State Highway 1 south of Rakaia.
A Southern Fire Service spokesman said the crash, about 1km south of Rakaia, happened after 5am. Three fire crews were at the scene.
Police said the critically injured person will be flown to Christchurch Hospital.
The Serious Crash Unit is on the scene and the road is expected to be closed for some time.
Diversions are being put in place and motorists are asked to avoid the area.
