Parisians and holidaymakers strolling along the banks of the River Seine or browsing open-air markets in Paris must wear a mask from Monday (August 10).
The order applies to people aged 11 and over - and covers busy outdoor areas in the French capital.
Though tourist sites such as the Eiffel Tower, the Arc de Triomphe and Champs-Elysees boulevard are exempt.
On Monday, many were confused about the exact locations where a mask must be worn - or had forgotten about the rules.
"I think it's a good thing. We're used to wearing one now, so why not just wear it? There are some places that have quite a lot of people, it's good to wear it so that we don't get infected easily."
"It's not clear at all. We're tourists, it's true that we don't know in which zones we're required to wear a mask. We assume that it's for places that are touristic, but right here, there are no signs, so it's quite unclear."
Data shows the virus has been circulating more widely in Paris and its lower-income suburbs since mid-July.
France made it compulsory to wear a mask in closed public spaces such as shops and banks since July 21.
Paris now joins a growing list of French cities ordering people to wear them in certain outside areas.
Those breaching the order face a fine of 135 euros.
But authorities said they would leave a bit of time before issuing fines so people can get used to the new rules.