French Prime Minister Jean Castex has responded to a steep increase in infections with a series of measures including increased testing and compulsory face-coverings in Paris.
The number of “red zones” where the virus is in active circulation has risen from two to 21.
If France did not act fast, the spread could become “exponential”, he warned.
A number of European countries are seeing a new surge in cases, and Germany is also planning tighter rules.
France has recorded its highest number of new daily infections since the end of the lockdown in early May, with an additional 6,111 registered over the past 24 hours.
A further 48 deaths were announced on Thursday, but mortality figures for Wednesday had not been available because of an IT problem. Overall, more than 30,500 people have died and nearly 300,000 have been infected in France.
Mr Castex said Covid-19 was “gaining ground” across the country. There was an “undeniable resurgence of the epidemic”, he said.
Promising to do everything to avoid another widespread lockdown, the prime minister said wearing a mask would become mandatory in the capital.
While individual streets and areas in the capital already have rules on wearing face-coverings, this new rule will be far more extensive, covering not only Paris but its inner ring of Seine-Saint-Denis, Hauts-de-Seine and Val-de-Marne.
From 08:00 on Friday (06:00 GMT), all pedestrians will have to wear face-coverings in public areas, as well as people on bicycles, motorcycles, scooters and a variety of other mobility vehicles.
Paris is already a red zone, along with the southern area of Bouches-du-Rhône, where France’s second city Marseille made masks compulsory from Wednesday evening.
The whole inner ring is now a red zone too, along with a broad expanse of the southern coastal fringe and the Gironde area around Bordeaux.