"Red level in Var and Alpes-Maritimes. If you live in these departments, be vigilant, warn your relatives and friends and follow recommendations of the authorities", Castaner wrote on Twitter.
He added that relevant agencies were working at the scene to help people.
According to the BFMTV channel, hundreds of people have been evacuated due to heavy rains in the department of Var. At least 1,300 homes have faced a blackout, with trains also running with delays.
Most recently, last week, France faced another weather anomaly when hundreds of thousands of homes suffered from a power outage amid heavy snowfalls in the region of Auvergne-Rhone-Alpes, southeast-central France.