The fire broke out on Monday evening in Lozère, in the south east of the country, and by Tuesday morning had burned 700 hectares of land and reached the neighbouring département of Aveyron.
A total of 600 firefighters are deployed in the area, plus helicopters, and there are no reported injuries.
The cause of the fire is believed to be sparks from an agricultural machine that was working in the area.
The fire is just the latest in a series to hit France this summer, including a huge blaze at Dune du Pilat in south west France, which burned for more than two weeks and destroyed an area of forest twice the size of Paris.
This is the worst year on record for wildfires in France, with the European Forest Fire Information System estimating that 47,000 hectares have burned since July – a total area five times the size of Paris.
France is experiencing an exceptionally hot and dry summer, with drought warnings in place for much of the country, which firefighters say has turned much of the country into a ‘tinderbox’ with a very high risk of wildfires.
In the south of the country many local authorities have imposed extra restrictions on access to forest areas and banned the use of fireworks.