The first case of a new coronavirus variant that recently appeared in Britain has been confirmed by France, its health ministry said.

More than 50 countries have been prompted to place travel restrictions on the UK by the current strain of the virus, which experts say is more infectious.

The first French case is asymptomatic and self-isolating at home in Tours in central France, the ministry said late Friday, discovered in a person living in Britain who arrived from London on December 19.

They were checked on December 21 in a hospital and later found positive for the strain.

Contact-tracing for the health practitioners taking care of the patient has been carried out by health authorities, the ministry said in a statement.

Similarly, any of their contacts that were seen as weak will be isolated, it said.

In addition to this first instance, several other positive samples "may suggest that the VOC 202012/01 variant is being sequenced" by the National Pasteur Institute's specialist laboratories, the statement added.

Olivier Veran, France's health minister, admitted on Monday that it was probable that the newly discovered strain was already in the country.

The Italian authorities detected a new strain in a patient in Rome, while nine cases were detected in Denmark and one in the Netherlands and Australia, confirmed by the World Health Organization.

Following this week's snap 48-hour ban, France reopened its borders to the UK, partially to allow French people to return home, as well as to ease the huge build-up of freight goods, but a testing policy was imposed.

The Ministry of the Interior of France said Thursday that travel limits from the United Kingdom would continue "until at least January 6."

For now, only citizens of France or the EU, residents there, or business travelers are permitted to cross from the United Kingdom, and only if the COVID-19 negative test can be shown to be less than three days old.

The new viral strain "may be up to 70% more transmissible than the original version of the disease," British Prime Minister Boris Johnson has said.

British Health Minister Matt Hancock declared before Christmas the extension of strict lockdown measures to contain the spread of the disease across other areas of southern England.

The United Kingdom is one of the hardest-hit countries in Europe, with over 68,000 deaths from the virus.