Another eyewitness described the "carnage" as multiple cars swerved and crashed on the busy road.
The woman, who asked not to be named, said she "luckily" saw hazard lights ahead as she approached on the slip road from Carterton, and moved on to a grass verge.
"I saw cars going zooming past me and trying to swerve out the way of the stationary cars but crashing into them," she said.
"I saw one car try swerve in between a Mini and another car, ending up crashing into the Mini and (flying) up in the air.
"I saw two cars swerve as they braked so hard and go flying into the barrier in the middle of the road ... it was carnage."
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