Wearing a face mask will be mandatory from Monday in busy parts of Paris amid a rise in coronavirus infections in and around the French capital.
Police said the order would apply to people 11 years and older in “certain very full zones”.
The virus had spread more in the region since mid-July, they said. Face masks are already required in enclosed public spaces.
Experts have warned that France could lose control of Covid-19 “at any moment”.
Several cities, such as Nice and Lille, have introduced their own additional orders requiring mask wear in certain outlying areas.
The Paris authorities have not yet specified which areas will be affected by the new order, which will come into force on Monday at 08.00 (06.00 GMT).
The zones where masks are required are being evaluated on a regular basis, they said.
In a statement on Saturday, authorities said the rate of positive testing for coronavirus was 2.4% in the greater Paris area, compared to the national average of 1.6%.
She added that 400 people tested positive for coronavirus every day in the region, with those between 20 and 30 years old being particularly affected.
Officials said earlier this week that they were calling for new measures for masks in the French capital.
“It simply came to our notice then [mask-wearing] be required in crowded open spaces and where the distance of a meter between people is difficult, “said Anne Souyris, the acting mayor in the service of health.
The new order comes after government scientific advisers on Tuesday warned that France could lose control of the virus “at any time”.
France reported 2,288 new coronavirus infections in its daily figures on Friday, marking a new post-lockdown high.
In total, the country has recorded more than 235,000 cases of coronavirus and more than 30,000 deaths, according to data collected by Johns Hopkins University.