The 16-year-old, who was in a serious condition in Dunedin Hospital last night, was the sole occupant of a Toyota Corolla car heading towards Mosgiel.
It appeared to have crossed the centre line and collided with a late model Holden car with four passengers heading towards Dunedin, witnesses said.
Emergency services were called to the crash scene, 300m west of Halfway Bush Rd, at 4.35pm, Sergeant Chris George, of Dunedin, said.
A passenger from the other vehicle was also taken to hospital for observation, Sgt George said.
Three Mile Hill Rd was closed from 5.30pm with a diversion along Dalziel Rd, before reopening at 9pm.
The serious crash team had investigated the crash and it was too early to say what caused the accident, he said.
Dunedin City Council roading and maintenance engineer Peter Standring confirmed the anti-icing chemical calcium magnesium acetate (CMA) had been sprayed on the road by council contractors at 11.30am.
"It is a bit [more] slippery than water," he said.
It is unclear if the anti-icing agent had contributed to the accident, but the council would co-operate fully with investigators, Mr Standring said.
