David Lewis, 48, and Melanie Keeling, 51, spotted dark smoke starting to billow from the engine bay of their Renault Megane Scenic moments after they got out the car.
As the pair scrambled to safety the car blew up, spraying broken glass and debris everywhere.
The blaze spread to two other parked cars as well as damaging a number of other vehicles.
Melanie and David had bought the 2006 Megane from a private dealer just three months before the incident and were told it had been fully serviced.
Melanie said: “If we were in that car for another 30 seconds we would have gone up in flames with it.”
A Renault spokesman said: “To date, Renault UK has not had any contact from either the customer or the insurance company regarding this incident with a 2004 Renault Scenic.
“Without having seen the car and without an understanding of the vehicle’s condition and service history, we cannot say what may have caused this incident and therefore we cannot comment any further.”