As hospitals run out of intensive care beds, France has been forced to put Paris and other northern regions into a fresh lockdown.
All non-essential shops will be closed, travel between regions will be banned, and forms needed to justify leaving home.
Schools, however, will remain open and limited outdoor exercise allowed.
The new measures, which will last a month, mark a hardening of the nightly curfew that's been in place since mid-December.
When announcing the restrictions, Prime Minister Jean Castex warned the country was in the grip of a third wave:
"The virus has been accelerating for 15 days now, the pressure on hospital systems has increased for a week, the time has come to face the consequences. This means that the measures we are taking today in the most impacted regions could be extended, if necessary, to other areas."
There are currently more COVID patients in intensive care in Paris than at the peak of the second wave.
France recorded 35,000 new cases on Thursday, with the highly contagious UK variant making up 75% of new infections.
President Emmanuel Macron had previously resisted calls for another lockdown wishing to protect the economy, but was forced to change course, owing to the new variant and a faltering vaccine roll-out.
This week France and other European countries briefly suspended the use of the AstraZeneca/Oxford University vaccine.
France is due to resume administering doses on Friday.