Danish health authorities on Sunday reported a “concerning” jump in cases of the omicron coronavirus variant that they said points to community spread in Denmark and probably elsewhere in Europe.

The number of confirmed cases in the country rose from 18 on Friday to 183 on Sunday, reflecting both the speed at which the variant has spread and the sensitivity of Denmark’s virus surveillance system.

The northern European country is a leader in the sequencing of variants, acting as an early-warning system for the continent. The rise in confirmed omicron cases there could be an indication that the variant has spread more widely throughout Europe than previously known.

Before the Danish data was released Sunday, the European Center for Disease Prevention and Control reported just 182 cases of omicron across all of the European Union, plus Norway and Iceland.

“Everybody is tested very frequently in Denmark with a very sensitive system, so if you were to do that in other European countries, you would likely find many more cases,” Troels Lillebaek, chairman of Denmark’s national coronavirus variant assessment committee, told The Washington Post.

“It’s not like Denmark is a special home for omicron.”

Health authorities in the country of 5.8 million perform more than 200,000 polymerase chain reaction, or PCR, tests per day — one of the highest rates of tests per capita in the world. Positive tests are submitted for special PCR tests that detect variants. For those that come back positive, scientists sequence the whole genome. Denmark sequences 25,000 strains per week, Lillebaek said.

In part, the surge in cases over the weekend reflects an updated accounting system, Lillebaek said. When omicron emerged, Danish scientists adapted the variant PCR test to detect it accurately. At first, they did not include cases that had not gone through full genome sequencing in the “confirmed” category. Now, scientists are convinced that their variant PCR test is reliable enough for omicron that they have begun counting positive variant PCR tests as confirmed cases.

Omicron, which contains a panoply of mutations, has generated alarm across the world. The variant was first flagged for global attention by South Africa, another leader in variant sequencing. News of the fast-spreading variant prompted more than two dozen countries to impose bans on travel from southern African countries — but by that point, it had already made its way around the world.

The ECDC said Sunday that omicron had been reported in 17 countries in the E.U. and the European Economic Area.

The center noted that “the majority of confirmed cases have a history of travel to countries in Africa.” But some of the new cases reported in Denmark had no apparent connection to southern Africa.

“There are now chains of infection where the variant is found in people who have not traveled abroad or been in contact with travelers,” Henrik Ullum, chief executive of Denmark’s Statens Serum Institut, which conducts the sequencing, said in a news release.

Danish media reported that some of the infections were traced back to a concert in late November and a Christmas lunch involving 150 guests.

Britain also reported a sizable uptick in omicron cases: 86 new cases on Sunday, bringing the total number there to 246.

Much remains unknown about the variant, including the danger it poses. Scientists around the world are racing to gauge its ability to get around existing vaccines and whether it causes severe disease. So far, omicron appears to be highly contagious. Lillebaek estimated that it could overtake the delta variant in Denmark and elsewhere in Europe in a matter of weeks.

Denmark, where 76 percent of people are fully vaccinated, will offer an important test for how omicron behaves in a highly vaccinated population. Danish public health authorities are speeding up vaccinations for residents aged 5 and older and booster shots in an effort to stave off its spread.

“We are still able to delay the spread of omicron while accelerating vaccines, but at some point it will be difficult to delay omicron,” Lillebaek said.