A major emergency is unfolding as a car engulfed in flames on Kwinana Freeway causes traffic chaos heading northbound towards the city.

DFES crews are working to contain the fire which broke out at about 7am Wednesday.

A lane of traffic at Bibra Lake is blocked, with traffic heavy back to Berrigan Drive.

Drivers are urged to drive with extreme caution and merge safely.

The cause has not been confirmed but its believed a possible mechanical fault could be to blame.

More to come.