A police spokeswoman said one person was moderately injured and another had minor injuries.
By 11am, the NZTA said congestion was beginning to ease.
Meanwhile, emergency services are also at the scene of a single motorcycle crash on the Princes St, Otahuhu, off-ramp, southbound, on the Southern Motorway.
Police had attempted to stop the bike, which then fled and crashed shortly after.
The motorcyclist is reported to have moderate injuries.
The road will be closed for some time while the Serious Crash Unit examines the scene, and diversions are in place.
Motorists should avoid the area and take an alternative route if possible, a police spokeswoman said.