The huge blaze caused the evacuation of more than 500 people in the Gironde region on Monday, as a smaller fire burned south of Bordeaux, near Dax, where temperatures reached 39C.
Strong winds hampered the efforts of hundreds of firefighters, who struggled to extinguish the flames throughout the night into Tuesday with little success. The fires are still uncontained.
Two Canadair aircraft have been deployed to help, alongside helicopters and a Dash plane.
It came as forecasters announced record temperatures in France for the month of December, with the mercury reaching 39.C in the southwestern Landes region.
Across Europe, an area equivalent to one-fifth of Belgium has been ravaged by flames as successive searing heatwaves and a historic drought propel the continent towards what experts say is likely to be a record year for wildfire destruction.
According to data from the European Forest Fire Information System (Effis), 659,541 hectares (1.6m acres) of land burned across the continent between January and mid-August, the most at this time of year since records began in 2006.
The figure is 56 per cent higher than the previous record in 2017. Then, 420,913 hectares burned over the same period, and 988,087 were consumed by the end of the year. On present trends, more than 1m hectares could be lost to wildfires this year.
The total land area burned across Europe so far this year is double the 2006-21 average, the Effis data shows, while the cumulative number of fires is more than four times the average over the same period.
Spain has so far been hardest hit, losing 244,924 hectares, followed by Romania (150,528) and Portugal (77,292).
More than 60,000 hectares have burned in France, half as much again as the 43,600 it lost in the whole of 2019, its previous record.