St John Ambulance said one person was in a critical condition and a second was suffering serious injuries.
Motorists are being warned to avoid the area with diversions in place, including for buses.
Fire and Emergency northern shift manager Craig Dally said a motorist was trapped in the wreckage of one of the crashed vehicles.
Fire crews were presently working to get the injured person out using cutting equipment.
Dally said there was also another person injured in the crash.
The accident happened at 6am.
A police spokesman said authorities were working to re-open the road as quickly as possible. However, the road was expected to be closed for some time.
The Serious Crash Unit was investigating the accident.
Meanwhile, on the Northern Motorway a rush hour crash had left a lane blocked and traffic building heading into the city near the Greville Rd on-ramp.
The New Zealand Transport Agency warned motorists to pass the crash scene with care and expect delays.