Weather agency Météo France has placed the Hérault department in southern France on red alert - the highest alert level - warning of "exceptional rainfall".
It urged residents not to travel about anywhere inside the department, especially not by foot or by car where a road is flooding.
Schools in the area have already been closed as a precaution.
The agency urged the public to take preventative measures to protect houses from flooding, even if they're not situated in areas prone to flooding.
Hérault on Wednesday afternoon. Photo: AFP
Some areas in western Hérault have already been hit by 150 mm of rainfall and winds of up to 110 km/hr, the agency noted.
Hérault is expected to get another 200 mm of rainfall before Thursday, with intense periods expected to bring up to 100 mm in just a few hours.
Another four departments were placed on orange alert, the second highest warning level that asks the public to be "very vigilant".
Those on alert are Aude, Bouches-du-Rhône, Aveyron and Gard.
The agency predicted strong storms and violent winds, and warned residents of potential basement flooding and disrupted traffic.
In nearby Nice, the bad weather prompted authorities to postpone Friday's planned memorial for the victims of the Bastille Day attacks until Saturday.
The agency added that rough seas could prompt coastal flooding and overflowing rivers.
Those in the area have been warned to be vigilant with any outdoor activities, and to avoid using the telephone and electrical appliances.