A 17-year-old girl remains in intensive care in Dunedin Hospital after a high-speed crash which killed a brother and sister from Mosgiel.

Danielle Ngametua Kiriau (17) and Shannon James Kiriau (22), of Mosgiel, were killed in the crash on Dunedin's Southern Motorway early yesterday morning.

At a press conference this afternoon police said the 20 year old male driver of the car remains in a stable condition in the High Dependency Unit in Dunedin Hospital while a 17 year old female passenger remains in intensive care.

The remaining 16-year-old female passenger has been discharged.

Police 'gutted' by deaths

Dunedin police are ''gutted'' by a high-speed double-fatality crash on the Southern Motorway that occurred on the same night as a comprehensive police traffic operation.

Clutha-Taieri area response manager Senior Sergeant Alastair Dickie said the deaths early yesterday could have been avoided.

Three other young people were hospitalised after the crash.

The police operation, focusing on speed, alcohol, restraints and dangerous driving, was held in Dunedin on Saturday night, and road checkpoints and pub visits were mostly in rural areas.

''Last night there was quite a bit of police activity in the city as well,'' he said yesterday.

''They have, unfortunately, managed to get through. We can't be everywhere.

''It's gutting really, because we've had quite a bit of resources put into it, and then we get this.''

The accident occurred when the driver of a Honda Integra car, with four passengers, lost control of the vehicle as it was heading south on the Southern Motorway about 3.15am.

The car was travelling around a right-hand bend at what police estimate was 180kmh (based on skid-mark evidence) near Green Island, when it spun several times before striking a light pole and a tree.

The female teen and the male front-seat passenger were pronounced dead at the scene.

Snr Sgt Dickie said the other occupants of the vehicle were taken to Dunedin Hospital. One, a female teen, is in a critical condition while the other two occupants, the male driver in his 20s and a 16-year-old female, received moderate to serious injuries.

Dunedin police were considering whether to lay charges against the driver, believed to be from Milton, once investigations were complete, he said.

Snr Sgt Dickie said the fatal accident was a culmination of several factors.

All five occupants had been drinking alcohol, and none of the three females in the back seat was wearing a seat belt. All were thrown from the car. The car had not had a warrant of fitness since early 2012 and had been ''green stickered'', ordered off the road until appropriate repairs had been made.

''We feel for the families,'' Snr Sgt Dickie said.

''It's probably a bit unfair to say under the circumstances, but we have to get this message home somehow, for the sake of others.

''They did everything wrong. There's been a few rules broken here, and it's ended up in disaster.

''One of them was speed, highly excessive speed. It was estimated they were going about 180kmh.

''The driver has been affected by alcohol and the back-seat passengers were not wearing restraints, which is a serious issue again.

''The car had been green stickered, which means faults had been found with the car and they had to be rectified before the sticker could be removed.''

Snr Sgt Dickie was not aware of the reason for the green sticker, but said a turbo-charger had been added. ''It had been modified, but it hadn't been certified.

''Really, a car like that, there's enough power without having things like that being added to it.

''Speed kills, and this is a good example of it.''

Snr Sgt Dickie praised the actions of two taxi drivers who were first on the scene and performed CPR on one of the victims.

He said the accident had been particularly harrowing for many of the police, fire and ambulance staff.

''I did note that the other emergency services at the scene were very affected by this. It was a pretty solemn scene really.

''I guess it was because the victims were of such a similar age to their own kids.''

The accident comes after several other recent fatal accidents around the regionThe southbound lane of the motorway was closed for most of the morning while an investigation into the cause of the crash was carried out.

-john.lewis@odt.co.nz