The two people killed when an unroadworthy car crashed at high speed in Dunedin last night were brother and sister, police say.
Police estimated the green stickered car, which should not have been on the road, was travelling at 180km/h before the crash.
The Honda Integra was heading south on the southern motorway with five occupants about 3.15am when the driver lost control while negotiating a slight right hand bend on State Highway 1 near Green Island.
The car spun several times before striking a light pole and a tree, police said.
The siblings from north Taieri - a male in his early twenties and a female in her late teens - died at the scene.
Police Clutha/Taieri area response manager, Senior Sergeant Alistair Dickie, said speed was a dominant factor in the crash.
"They saying 'speed kills' was quite evident in this case unfortunately."
Intoxication, lack of restraints and the condition of the vehicle were also key factors, he said.
"[The vehicle] had a turbocharger fitted to the motor and an intercooler to give it more power, but there's no evidence of it being certified."
The vehicle was not up to Warrant of Fitness standard and had been green stickered - meaning it had faults which needed to to be repaired before being allowed back on the road, he said.
The police serious crash unit estimated the car was travelling at 180km/h when the vehicle crashed.
"There were three girls in the back seat that were ejected from the vehicle, one of them died and one is in a critical condition in Dunedin Hospital.
"The other deceased was the front, left-hand passenger. He's sustained injuries from inside the vehicle."
The other passengers, a male in his 20s and a 16-year-old female, suffered moderate to serious injuries and were also at Dunedin Hospital.
Charges against the driver were being considered, Mr Dickie said. "We're still following an investigation but it's certainly shaping up that charges will be laid."
"Young people have just got to think about what they do when they get in a car and they've got to think about the basic rules because it certainly in some cases means the difference between life and death."
The names of the deceased would not be released until their next of kin had been notified.
Anyone with any information about the crash were asked to call Dunedin Police on 03 471 4800.