Prime Minister Jean Castex urged France on Monday to remain as vigilant as possible against COVID-19, which has shown signs of a resurgence in the country, as the virus was "not on holiday".
"We must not let our guard down," Castex told reporters in Lille, where masks are now compulsory in many of the northern city's pedestrian areas and parks.
"The virus is not on holiday, and neither are we," he said, adding it was vital that France avoided another nationwide shutdown.
The southern city of Nice on Monday also made wearing masks outdoors compulsory in many areas, including parts of the Promenade des Anglais, a popular tourist spot.
France has the world's seventh-highest COVID-19 death toll, at just over 30,260 fatalities.