Six St John vehicles attended the crash and four people were transported to Middlemore Hospital.
The southbound lanes were blocked for a short time before reopening about 12.30am.
One Aucklander, who was travelling home and witnessed the aftermath of the crash, said the occupants of one of the cars were "lucky to still be alive" as it appeared the roof had caved in.
Another person who witnessed the scene was "amazed" that no one died given the severity of the crash.
"The engine was torn from its mounts and the entire front driver's wheel and strut ripped out and [was] thrown up the road," he said.
It preceded another crash in Te Awamutu where four people were hurt with one in a critical condition after a car crashed into a tree.
Emergency services were notified of the single-vehicle crash about 12.20am.
The incident occurred at the roundabout at the intersection of Ohaupo and Cambridge Rds.
Four people were injured – one was in critical condition, another in a serious condition, and two others in moderate conditions.