France announced on Sunday that it has implemented a 48-hour ban on travel from Britain, joining a growing number of European countries halting travel from Britain after a new strain of the coronavirus was detected in that country. At least six European countries have announced flights will cease if they haven’t done so already, while France and Belgium have banned train travel.

French officials said the 48-hour stoppage would give them time to find a “common doctrine” to stop the spread of the new COVID-19 variant. French President Emmanuel Macron tested positive for the coronavirus on Thursday.

Germany, which holds the EU presidency, called a special crisis meeting for Monday to coordinate a response. 

Canada also announced U.K. travel restrictions on Sunday. Prime Minister Justin Trudeau said all flights from the U.K. would be “prohibited from entering Canada” for 72 hours. The travel ban does not affect cargo shipments.

Top health officials in Britain say a new, fast-moving variant of the coronavirus could be up to 70% more transmissible than previous ones. This strain appears to be driving the rapid spread in London and southern England. But there is no evidence the new strain is deadlier or would react differently to the vaccine, according to BBC News.

As a result of the new strain, Prime Minister Boris Johnson announced on Saturday a new tier of coronavirus restrictions, the strictest yet, and canceled the planned five-day Christmas relaxation period that had been planned from December 23 through 27.

“I know how much emotion people invest in this time of year, and how important it is for grandparents to see their grandchildren,” Johnson said Saturday. “But when the virus changes its method of attack, we must change our method of defense.”

Johnson also said the capital and other areas in southern England currently under Tier 3 — the highest level of coronavirus restrictions — will move to an even stricter new Tier 4 that requires all non-essential shops, hairdressers and indoor leisure venues to close after the end of business hours Saturday.

Videos went viral on Saturday night of Britons packing London train stations in a last-minute scramble to leave the city ahead of Christmas. British health secretary Matt Hancock described the rush to travel a “totally irresponsible behavior,” according to to Sky News.

U.S. Surgeon General Jerome Adams said on “Face the Nation” on Sunday that the National Institute of Infectious Diseases, the Centers for Disease Control and the World Health Organization are investigating the new strain. But he stressed that even if it is found to be more contagious, it reinforces the importance of following existing social distancing guidelines.

“Well, very important for people to know that viruses mutate all the time, and that does not mean that this virus is any more dangerous,” Adams said. “We don’t even know if it’s really more contagious yet or not or if it just happened to be a strain that was involved in a superspreader event. Right now, we have no indications that it is going to hurt our ability to continue vaccinating people or that it is any more dangerous or deadly than the strains that are currently out there and that we know about.”

The Associated Press contributed to this report.