She said many drivers were out of their cars standing on the road as traffic was simply not moving.
Another said traffic was backed up to Westgate Shopping Centre on the city bound side of the motorway, and backed up to the city on the other.
At about 7.10pm NZTA tweeted that the motorway was open, but down to one lane. It had been "completely blocked".
"Tail will take time to clear," a spokesperson said.
Police were currently removing the damaged cars and an investigation into the crash was ongoing.
Fire Service northern communications shift manager Scott Osmond said staff were called to the incident about 6.15pm.
"There was one person trapped with a spinal injury."
Staff freed the injured person and left the crash scene after about 30 minutes, he said.