The white car clipped another car, causing that one to clip another car. The white car then did a U-turn and carried on travelling south in the correct lanes.
Police estimate it drove the wrong way on the motorway for about 2km.
Driver Fleur Koorey said she had her kids in the car with her as she drove home from Porirua, when she saw the car ahead of her braking.
Koorey was in the passing lane when she suddenly saw the white car heading toward her.
"I had to quickly swerve into the other lane to avoid hitting it basically, so yeah, slowed right down and yeah, it was a bit freaky," she said.
"I looked in my rearview mirror and it was still going.
"It just happened so quickly."
Koorey was "stumped" as to how it ended up going the wrong direction, but said she'd once seen a car heading the wrong way down a nearby ramp at Grenada, so wondered if the driver could have done the same thing.
She was unsure how fast the car was going, but said she was doing 100km/h herself.
"The old adrenaline kicked in and stuff," she said.
Stephen Riden also witnessed the car going the wrong way.
"I was in the inner lane overtaking another car on a series of curves past Tawa, heading towards Wellington," he said.
"The white car was moving along the inner barrier but not at high speed."
Riden had to brake and move half out of his lane to avoid the car.
"It was a surprise to say the least."
Facebook user Anna Win-Mason said the driving was "absolutely dangerous behaviour".
"We almost crashed our car because of that insane driver," she wrote.
"Luckily saw them in time, and the car stopped just in front of them. It was getting dark with heavy rain at the time this incident happened. Plus ahead of us there were about 4 cars that must have swerved out the way and were haphazard on the road too, must have been due to this stupid illegal manoeuvre."
Ben Huijs was in the back of a car heading into Wellington when he heard his friend say there was a car coming the wrong way.
Next minute the car in the right lane swerved in front of them to avoid the oncoming car.
He said it almost caused them to crash into the barrier.
Huijs said they soon passed a car that was sitting on the motorway facing the wrong way, looking "pretty smashed up".
They saw about three or four other cars parked up on the side of the road, some of which appeared to be dented.
Police are making inquiries into the actions of the white car, however are also seeking further information from the public.
Anyone who saw this vehicle or has information that may assist police in locating it is asked to email Constable Martin Kelly at mkaj73@police.govt.nz
