The fire began in the commune of Generac south of Nimes in the afternoon and spread over 250 hectares (124 acres) as of the evening, according to the Le Provence newspaper.
Around 300 firefighters, 90 ground vehicles and seven planes have been mobilized to tackle the blaze. The smoke rising from the burning grounds can be seen 30 kilometers (19 miles) away.
The Mediterranean department saw dozens of fires erupt in the previous heatwave a month ago.
Record-smashing temperatures were reported in over 50 French cities last Thursday after sweltering weather returned.
Last week, the heatwaves across the continent reached the blistering peak, with Paris recording a temperature of about 109F (42C). Large swathes of Germany, Belgium, the Netherlands and the United Kingdom have also set their own temperature records.
Moreover, France, which has 58 nuclear reactors, has reportedly decided to temporarily curtail electricity output at several reactors to limit the heating of water which is used to keep reactors cool.