The collision between two vehicles on the A760 Largs to Kilbirnie Road happened at about 22:30 on Friday.
An 18-year-old man was driving a Nissan Juke towards Largs when he collided with a Ford Focus travelling in the opposite direction near Mills Dairy.
The 17-year-old female passenger in the Nissan died at the scene. The driver has serious chest injuries.
He is being treated at Crosshouse Hospital in Kilmarnock where his condition is described as serious but stable.
The woman who is in a critical condition was a passenger in the Ford Focus. Police Scotland said she had "very serious injuries" and is being treated at the Royal Alexandra Hospital in Paisley.
The 32-year-old driver of the Focus suffered minor injuries and has been released from hospital.
Police have appealed for witnesses to contact them.
A teenager has died and a 28-year-old woman is in a critical condition after a car crash in North Ayrshire.