France reported 4,897 new coronavirus infections over the past 24 hours on Sunday, the highest daily level since the end of a two-month lockdown in May.
Health Minister Olivier Véran warned earlier that the situation was risky, and said infections were essentially happening among 20 to 40 year-olds at parties.
Cases among older people were starting to rise too, Véran said, but he ruled out another total lockdown in France.
Sunday's health ministry figures showed the number of people in hospital edged down by two to 4,709 from the previous day, however. Three more people were registered in intensive care, taking that total to 383.
Total coronavirus deaths rose by one in the past 24 hours to 30,513. The country has recorded a total of 242,899 infections.
Infections primarily among people under 40
The coronavirus is circulating four times more among people under 40 in France than among over 65-year-olds, Véran said in an interview with France's Journal Du Dimanche (JDD) published on Sunday, adding that the higher number of cases being detected was not solely down to more testing.
Véran said the cross-contamination between groups of the population - younger people between the ages of 2 to 40 and their elders - was already taking place.
"New measures will be implemented shortly," he said, without elaborating.
Parties and gatherings where social distancing rules were not being respected were now the main source of contagion, Véran added, as opposed to earlier in the summer when it had been in the workplace.
In many cases, younger carriers of the virus were asymptomatic or suffered fewer complications, Véran said.
Police in Paris are gearing up for possible football celebrations Sunday night as Paris St Germain takes on Bayern Munich in the Champions League final, and officials said they would enforce mask wearing and distribute protective gear in sites like the Champs Elysee avenue.
(FRANCE 24 with REUTERS)