Europe is on edge as Omicron cases rise quickly before the holidays.

LONDON — Confirmed cases of the Omicron variant surged in Britain and Denmark on Sunday, backing up scientists’ fears that it has already spread more widely despite travel bans and adding to worries of new lockdowns before the holidays.

On Sunday, Britain’s health security agency confirmed that it had now detected 246 cases of the variant — nearly double the total number of cases reported on Friday. In Denmark, the local health authorities confirmed that there were 183 known cases of the variant, more than triple the total number of suspected cases reported on Friday, and called the figures “worrying.”

The numbers are skewed somewhat because both countries are widely seen as leaders in genomic sequencing and testing, so they are finding the variant in part because they are looking so carefully for it. And in Britain, scientists are focusing much of their genomic sequencing on international travelers and on contacts of those already infected with the Omicron variant — two groups more likely to have been exposed.

Still, the announcements make clear that the number of Omicron cases is rising quickly. What that might mean for public health remains less clear.

Michael Ryan, the head of the emergencies program at the World Health Organization, speaking last week at a news conference, said European countries should have taken more precautions this autumn to protect their populations.

“We will have to be a little patient in order to understand the implications of the Omicron variant,” he said, “but, certainly we are dealing with a crisis now. And that crisis is in Europe, and it is being driven by the Delta variant.”

Now, he said, it is time for “everyone to recommit ourselves to controlling the pandemic of multiple strains or multiple variants of the same virus.”

Many questions remain about the Omicron variant. Some early signs exist that it may cause only mild illness, though that observation was based mainly on cases in South Africa among young people, who are generally less likely to become severely ill from Covid. Scientists are also waiting to see whether cases lead to substantial hospitalizations and deaths; both are lagging indicators.

And at the moment, scientists say there is no reason to believe Omicron is impervious to existing vaccines, although they may turn out to be less protective to some unknown degree.

Emily Anthes, Thomas Erdbrink, Jasmina Nielsen and Holly Secon contributed reporting.