Police are trying to determine if two vehicles involved in a fiery freeway crash in Perth were racing each other.

A Ford Festiva, believed to be stolen, and a Suzuki Swift collided late last night on the northbound lane of the Kwinana Freeway just before the Narrows Bridge.

The Swift then burst into flames.

Passing motorists, including a registered nurse, pulled the 18-year-old driver from the burning car.

He was taken to Royal Perth Hospital where he is in a critical condition.

Two people from the Festiva were arrested and taken to hospital with suspected back injuries.

The teenage driver fled the scene.

Police are investigating whether the drivers of both vehicles knew each other and were travelling side by side before the crash.

The freeway between Canning Highway and the Narrows Bridge was closed overnight as a result of the crash, but has since reopened.

Police are appealing for anyone who witnessed the crash to contact Crime Stoppers on 1800 333 000.