Police investigating a fatal crash near Dunedin early on Sunday morning say the car had not been warranted since 2012.
A man in his 20s and a woman in her late teens were killed and three other people were injured when the car spun out of control on State Highway 1 near Green Island, just after 3am.
Senior Sergeant Craig Brown of Dunedin police said speed, alcohol and the condition of the car appeared to be factors in the crash. He said it also appeared that the car had been modified.
A teenage girl who was critically injured in the crash has improved and is now in a serious condition in Dunedin Hospital.
The driver of the car, a man in his 20s, remains in a serious condition in hospital while a teenage girl who was also a passenger has moderate to serious injuries.
Mr Brown said the driver lost control while negotiating a slight right-hand bend, and the car appeared to have spun several times before hitting a light pole and a tree.
He said it was believed three of the occupants were thrown from the vehicle.
The southbound lane of the motorway near Green Island was closed for several hours following the fatal crash.