Although the blaze at Saint-Cannat, near Aix-en-Provence, was brought under control on Sunday evening, about 800 firefighters were still putting out the last flames on Monday, soaking areas where underground fires could be continuing.
High temperatures and a southerly wind meant there was a risk of the blaze flaring up again, firefighter Nicolas Faure told the AFP news agency.
Officials have found no evidence that the fire, which started on Saturday, was caused by arson.
They believe it was started accidentally, probably by someone throwing a cigarette end onto the ground.
“People don’t realise the danger,” Faure commented.
Wilkdfires are an annual event in southern France and on the Mediterranean island of Corsica.