Large fires have already ravaged parts of Greece, Turkey, Spain, Portugal, Algeria and Morocco.
The blaze broke out Monday at a motorway stop about 60 miles north-east of the port city of Toulon.
By Tuesday morning, it had already covered more than 3,500 hectares of forest and scrubland, according to the fire department.
“This is the area covered but it is too early to estimate the area burned,” the spokeswoman said.
Evacuations have mainly taken place around Saint-Tropez and the villages of Le Mole and Grimaud, Ms Vienco said.
“The fire is very huge and its spreading at a speed of four kilometres an hour, it’s a very difficult battle.