The Omicron variant of the coronavirus is probably already circulating in France, its health minister said on Sunday, adding that the government was tightening restrictions to contain its spread.

Omicron is potentially more contagious than previous variants, although experts do not know yet if it will cause more or less severe COVID-19 compared to other strains.

"There is no identification yet, but it's a matter of hours," Olivier Veran told reporters at a vaccination centre in Paris.

"Once the variant is circulating in England, in Italy, in Belgium, it is probable that there are already cases in circulation here. We will identify them and (...) we will slow down its spread as much as possible."

France is the midst of a fifth wave of the virus. It recorded more than 37,000 positive cases on Saturday and a sharp rise in the number of patients in intensive care.

The Health Ministry recommended on Saturday the isolation of any contact person at risk of a possible case or a confirmed case of the Omicron variant, even vaccinated, in documents sent to establishments and health professionals, Agence France Presse reported.

Those people should be considered "high risk" and quarantined, the document said.

Until now, contact cases of an infected person had to be isolated only when they were not fully vaccinated or when they had weak immune systems.