Massive fire burns in Fontainebleau near Paris
The fire in the forest about 60 kilometres south-east of Paris had burned through 800 hectares by Monday morning and was still spreading.
Nearly 400 firefighters and two water bombing planes have been sent to contain blaze, which officials have described as "very virulent" and of "exceptional scale".
The forest, once a royal hunting preserve, is dotted with villages, and around 15 homes had been evacuated from the village of Vaudoue.
Without the firefighting planes, other villages would already have been evacuated, said Olivier Compta, who is overseeing the firefighting operation.
A6 highway shut down
The fire in Noisy-sur-Ecole has caused the partial closure of the A6 highway, the country's main north-south artery, causing travel chaos for people traveling ahead of the 14 July national holiday.
Eric Brocardi, of France's national federation of firefighters, said it was the first time the planes had been sent up from the normally drier and hotter south of France to extinguish fires in the Paris region, which like large parts of the rest of the country is experiencing its third heatwave since May, increasing the risk of fires.
Two firefighting helicopters and an observation aircraft were also helping to fight the blaze, Brocardi said.
Heatwave exacerbating fires
Interior Minister Laurent Nunez, whose office announced he would visit Fontainebleau on Monday, said that forest fires had already consumed 17,000 hectares this year.
Once the figures had all been tallied, that would come to 25,000 hectares, or "twice as much as the same period" in 2025.
Earlier, firefighters dealt with a fire that had blocked a highway running east from Paris and disrupted the TGV high-speed train line to the south of France.