The use of hospital beds by Covid-19 patients in the French city of Marseille is "close to saturation" amid a sharp spike in infections.
Surgeries are being reduced to cope with an incidence rate that has risen to 312 per 100,000 since September.
New limits on gatherings are being introduced around Marseille and in the south-western city of Bordeaux.
The two cities are the main new hotspots in a country that on Saturday recorded a big surge in cases.
The 10,561 new infections over 24 hours represented the biggest rise since large-scale testing began.
The figures for Sunday and Monday were lower - as tends to be the case for weekend reporting - but the seven-day rolling average, which smoothes out these irregularities, recorded an increase in infections for the 28th day in a row.
France has recorded more than 425,000 infections, and almost 31,000 deaths, in the coronavirus epidemic, Johns Hopkins University research shows.
Why the new measures?
On Friday, Prime Minister Jean Castex warned of "worrying developments" in Marseille and its department of Bouches-du-Rhône, and in Bordeaux. He called for new measures to be laid out by Monday.
At a briefing on Monday, Philippe de Mester, director general of the Provence-Alpes-Côte d'Azur health agency, said the rate of positive tests had reached 10.6% in Marseille and 8.5% in the Bouches-du-Rhône overall.
Intensive care capacity was close to overload. Marseille hospitals director Jean-Olivier Arnaud said 31 of 35 resuscitation beds and 129 of 155 dedicated Covid patient beds were in use, adding: "We are not far from saturation."
"We are at the top of the national ranking of departments whose situation is developing the most unfavourably," Mr de Mester said.
Yann Bubien, a Bordeaux hospital director and a member of the government's Covid scientific advisory council, said there had been "a very rapid increase over the past 10 days" in the city.
"All the warning signals are flashing red," he said.
What are the measures?
In Marseille and the Bouches-du-Rhône until 1 October:
- Large-scale gatherings for the public limited to 1,000 seated people, with minimum one-metre (3ft) distance
- Student parties banned and school outings suspended
- No private meetings of more than 10 people, including on beaches and in parks, in high-risk areas
- Masks compulsory in 27 high-risk areas in the department from 06:00 (04:00 GMT) to 02:00 (00:00 GMT), except in large outdoor areas
Very similar measures were introduced for Bordeaux, including the 1,000 limit on large-scale gatherings and 10-person limit on private meetings.
Additional police will be deployed to enforce the measures in Bordeaux, with the situation to be reviewed in "two or three weeks".
In addition, the Monte-Carlo International Festival, the biggest circus event in the world, scheduled for January, has been cancelled.