France will restrict arrivals from Britain because of fast-spreading cases of the omicron coronavirus variant, putting limits on reasons for travelling and requiring 48-hour isolation upon arrival, the government said Thursday.

The new measures will take effect first thing Saturday, just after midnight, “in the face of the extremely rapid spread of the omicron variant in the UK”, French Prime Minister Jean Castex said in a statement.

The French government is holding a special virus security meeting Friday that will address growing pressure on hospitals in France from rising infections in recent weeks. Delta remains the dominant variant in France, but omicron is spreading so fast in Britain that it’s raising concerns across the Channel.

French government spokesman Gabriel Attal said on BFM television that tourism or business trips from Britain to France “will be limited,” though French citizens will still be able to make the journey.

All those arriving from Britain will need to have a negative virus test less than 24 hours old, and to test again upon arrival and isolate “in a place they choose” for at least 48 hours pending the result, Attal said.

The measures will apply to vaccinated travelers as well as unvaccinated travelers.

The UK recorded the highest number of confirmed new COVID-19 infections Wednesday since the pandemic began, and England’s chief medical officer warned the situation is likely to get worse as the omicron variant drives a new wave of illness during the Christmas holidays.

According to France’s new measures, citizens of any EU country can still enter France from Britain, in addition to non-EU citizens with a long-term EU residency permit or long-term visa, and some other categories of people including truckers who are only transiting France, diplomats and health care workers.

People will be allowed to leave France for Britain only if they aren’t French, or if they have an urgent health or legal reason to travel.

The abrupt move comes after weeks of political tensions between France and Britain over post-Brexit fishing rights and how to deal with migration in dangerous small boats across the English Channel.

It also comes as France’s government is desperately trying to avoid a new lockdown or stricter measures that would hurt the economy and cloud President Emmanuel Macron’s expected campaign for the April presidential election.