Vehicles were crushed after a burst water pipe flooded an underground car park. A number of vehicles crumpled after polystyrene insulation under the floor appeared to float or swell, forcing them into the concrete ceiling above.
Flood water rose several feet at the newly-built car park below a block of flats in Crayford, south east London.
Residents said they had been warned if any of the cars were removed too hastily it could result in gas explosion.
Between 12 and 16 vehicles are thought to have been damaged.
One owner was told her car was written off as a result of the damage and might not be covered by insurance.
Sadia Farzana Chitra, 42, said: "My car is crushed, the roof is gone.
We were told we could not move it because there was a possibility that with the pressure of the car there could be a blast because of the gas inside.
It could have blown up the whole building."