Parks and gardens will also be closed nightly in a bid to prevent large gatherings of young people in particular, the government's top official for the region said late Sunday.
Authorities are on high alert across France as people travel for summer holidays, heightening the risks of new outbreaks as observance of social distancing rules wanes.
Last week, face masks became mandatory in all enclosed public spaces, and the government warned that localised lockdowns might be required.
On Saturday, testing for Covid-19 was made free without a prescription across France.
54 new cases
Quiberon, popular resort with families, recorded its first Covid-19 case last Tuesday. Less than a week later, that number has grown to 54.
The mayor moved quickly to make face masks mandatory in open-air markets and on busy streets.
"Nonetheless, in light of the fast-evolving situation, the mayor of Quiberon issued a decree to close beaches, parks and public gardens from 9:00 pm to 7:00 am," the government official said in a statement.
"The state services urge the entire population of Quiberon to sharply reduce their social contacts and respect preventive measures."
France, where the virus death toll stands at 30,192 victims, is currently registering more than 1,000 new cases a day nationwide, health authorities said Friday.
