Main South Rd remains closed as police make enquiries into the circumstances surrounding the crash.
NZ Transport Agency Waka Kotahi (NZTA) said SH1 at the North Rakaia Rd intersection is closed, with detours involving an extra 100km of travel.
Earlier, Hato Hone St John said three people had been injured, with one in critical condition.
One first-response unit, one operations manager, two air ambulance helicopters and two ambulances responded to the scene.
“Our ambulance staff treated three patients and transported two of them to Christchurch Public Hospital by helicopter, one in a critical condition and one in a serious condition,” St John said.
“The third patient was transported by road ambulance to Christchurch Public Hospital in a moderate condition.”
Police said the area around Main South Rd was blocked and would be for a significant period of time.
Police advised motorists to avoid the area and choose alternative routes as emergency services work at the scene.
The Serious Crash Unit has been notified.
NZTA said contractors are working to set up formal detours, with emergency services expected to continue working at the site for “several hours”.
“People are urged to avoid the area or delay their travel if they can.
“If people are in the area, they can consider travelling inland via State Highway 77 and crossing the river at the Rakaia Gorge.
“However, people should be aware this involves an additional 100km of travel between Rakaia and Christchurch, and SH77 may also be congested by other detouring traffic.”
