Emergency workers have rescued and evacuated hundreds of people in southern France as flash flooding abruptly turned roads and fields into rivers and lakes.

As new heavy rainfall threatened the area on Wednesday, the emergency service for the Gard region said rescuers were searching for at least one person reported missing after the Tuesday evening flood.

No casualties have been reported, but local authorities said the rains caused significant damage to homes and infrastructure across towns and villages between Nimes and Montpellier.

One person was hit by lightning but survived, and a supermarket roof collapsed under the pounding water, according to the regional emergency service.

People evacuated from a campground as they watched waters surge towards their campers, BFM television reported. About 800 firefighters were mobilised to rescue people via helicopter and other means.

Schools across the region were closed on Wednesday as clean-up work started in some towns.

The flooding comes after a season of extreme weather that saw devastating wildfires near the French Riviera and around the Mediterranean, record-breaking flooding in Germany and Belgium and droughts or heatwaves in other areas around the world. Scientists say such events are expected but happen more frequently now as the planet is warming because of human-caused climate change.