Beijing reported a pickup in new COVID-19 cases among those in China for the Winter Olympics on the day the games kicked off, highlighting challenges to contain the virus as more participants arrive.

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Official data showed 45 new cases were identified on February 4, more than double the previous day’s tally and compared to an average of 40 for the latest three days. The latest daily infections included 26 new arrivals who tested positive at the airport, and 19 who were already in the “closed loop that’s cut off from the broader population,” the Chinese committee organizing the event said in a statement.

An acceleration was expected as more Olympic-related personnel arrive in the Chinese capital for the games, Huang Chun, a top virus-control official at the organizing committee, said last week.

Those visiting the city for the event are being kept within a tightly controlled bubble. Authorities want to ensure that outbreaks in the broader population are not spread by travelers from abroad.

Olympics-related patients will be put into five different categories for separate treatment at different hospitals to avoid cross infection, according to Wang Jianhui, deputy director of the city’s disease control center.

Friday’s new cases included 25 athletes and team officials, with the rest from other participants including journalists and diplomats.

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