France’s prime minister, Jean Castex, announced last week that a curfew imposed on Paris and eight other cities would be extended to 38 more departments.
It confines 46 million of the country’s 67 million people to their homes from 9pm to 6am.
"A second wave of the coronavirus epidemic is now under way in France and Europe. The situation is very serious," Mr Castex said at a news conference.
Shortly after the measures were announced, French health authorities reported a record 41,622 new confirmed cases, bringing the cumulative total to 999,043.
It comes as a government scientific adviser warned the virus was spreading through France faster than at the peak of the first wave in spring.
"The virus is circulating more quickly than in the spring," epidemiologist Arnaud Fontanet, who sits on the Scientific Council advising the government on its Covid-19 response, told BFM TV.
He said France’s three-month-long lockdown had brought the virus under control but also resulted in a false sense of security during the summer.
By late July, the country’s caseload was trending higher again, though it was a cold snap that appeared to have altered the disease's trajectory, Mr Fontanet added.
"There was one cold week in September and all the indicators went the wrong way again all over Europe. The virus spreads better in the cold because we live more inside," he said.
"It is possible the second wave will be worse than the first," Martin Hirsch, head of public hospitals in Paris, warned on RTL radio. "No one can say when the peak will come."
According to a Reuters tally, Wednesday saw the highest total of infections reported in a single day aross the world, at 422,835.
More than 5.3 million people across Europe have contracted the disease and over 204,000 have died, according to the European Centre for Disease Prevention and Control. That compares with 8.3 million cases in the United States and 7.7 million in India.