Both drivers were seriously injured after a head-on crash on a motorway at Wainui, in the Auckland region, this morning.
One of the vehicles was a stolen Toyota Aqua and being tracked by the police's Eagle helicopter.
Moments before the crash, police said the driver entered the Northern Motorway at the Wainui off-ramp and drove against the flow of traffic.
"The car travelled roughly 50 metres before it collided with an unsuspecting member of the public, who effectively had no time to react," Inspector Danny Meade said.
The crash happened about 6.20am and led to a two-hour-long closure of the motorway.
The vehicle being tracked had been stolen from a property in Constellation Dr overnight and was spotted in Westgate about 5.35am.
Eagle located the car and kept watch as it drove along State Highway 18 and onto the Northern Motorway.
"Near Oteha Valley Road, police signalled to the driver to stop, but the vehicle allegedly fled at speed," Meade said.
He said officers didn't pursue, however "Eagle kept tracking the car, relaying its movements through a subdivision in Wainui."
"While officers on the ground were preparing spike strips, the driver, for some unknown reason, entered the motorway in the wrong direction.
"It is incredible that nobody died."
The Serious Crash Unit carried out a scene examination and the motorway reopened about 8.15am.
Meade said the investigation into the crash was continuing and both drivers were being treated in hospital.
Charges were being considered against the youth alleged to have been driving the stolen Toyota.
