A driver escaped without injury after pulling over on the A3 at Tolworth, as his BMW burst into flames.
Firefighters and police were called to the blaze on the northbound slip road shortly after 6pm yesterday.
Surbiton fire crew manager Ian Meyer said the fire was put out within just a few minutes.
He added: "I've never seen a car go like it before. It was quite big.
"It had some kind of mechanical fault. The fire started in the engine compartment.
"The whole of the front of the car was going well."
Police cordoned off the stricken 5-Series luxury car as firefighters spent an extra half an hour making sure the flames were out.
Did you see what happened? Contact the newsdesk at email@example.com.