An early morning crash which killed two people and left two others in a critical condition was caused by a vehicle travelling 10km in the wrong direction.
CCTV footage has confirmed the offending vehicle had entered the Wellington Urban motorway northbound lanes at Petone.
Two vehicles collided in the northbound on the fly-over between Molesworth St and the Aotea on-ramp, at about 4.20am.
Two people died at the scene and the two in the second vehicle were taken to Wellington Hospital. One is in a serious condition in ICU, and the other is undergoing treatment, said a spokesperson.
After reviewing CCTV police have confirmed the vehicle in which two people died had entered the motorway by turning right into a northbound lane from Cornish St in Petone.
A woman driving to work told the Herald she saw a car driving on the wrong side of the motorway.
"My co-worker was also coming to work at this time and saw far more than me - [he] was trying to signal the driver to turn around."
The woman said her colleague had seen the car get onto the motorway via the Petone entrance before it "sped off".
"[My colleague] was trying to alert oncoming drivers by flashing high beams and hazard lights."
The woman got off the motorway at the Aotea off-ramp and did not see another vehicle.
"The crash seems to have happened just after that," she said.
"It would've been just before 4.30am as that is when I started work."
The woman said her colleague suspected there was a possibility the driver going down the wrong side of the motorway had become confused about where they were going.