Two teenagers are dead after a car crossed the centre line on State Highway 1, near Amberley in North Canterbury.

The driver of a car that caused a double fatality in North Canterbury was driving illegally.

Two 16 year olds, one male and one female, were killed in a "horrific" head-on crash on State Highway 1, two to three kilometres north of Amberley, north of Christchurch, shortly after 6am on Sunday.

Three teenagers were heading south in a white Nissan Silvia when the car crossed the centre line and collided head-on with a black Holden Colorado, according to police. The crash brings the 2018 road toll to 86.

JOSEPH JOHNSON/STUFF Police say the white vehicle crossed the centre line before hitting a northbound 4WD.

It is understood the driver was on a learner licence and had been travelling back from Nelson after picking up the car there.

A learner licence prohibits drivers from carrying passengers unless they are a supervisor who has held a full licence for two years. None of the teenage passengers could have met this criteria because a full licence cannot be granted until age 18.

One teenager was taken to hospital with what was understood to be a head injury, but in a stable condition.

JOSEPH JOHNSON/STUFF The scene of a crash which killed two teenagers on Glasnevin Road, State Highway 1, in North Canterbury.

Two men in the Colorado, heading north, were taken to hospital. The driver was later reported to be in a stable condition and the passenger, comfortable.

A woman, who did not want to be named, said she was one of the first on the scene.

"I was travelling behind a white car that came up Ardross Hill towards Amberley and crossed the centre line, smacking into a 4WD," she said.

JOSEPH JOHNSON/STUFF Two teenagers are dead after a crash involving a car and a 4WD near Amberley in North Canterbury.

"Out of respect to the families I won't give out details. It's a horrific sight that I will have to live with for the rest of my life, but I am grateful and very thankful I am alive and unhurt."

Sergeant Rene Pabst said police were trying to work out the cause of the crash.

GOOGLE MAPS Emergency services raced to the crash on Sunday morning.

"That's going to be part of our investigation, to establish the reason they crossed the centre line," he said.

Police inspector Peter Cooper said police would speak to the crash survivors on Monday.