(Bloomberg) -- China reported its worst week of Covid infections since mid-May, fueled by outbreaks in vacation hotspots that risk spreading across the country as travelers return.

The country reported 2,678 cases for Thursday, down from 3,424 a day earlier. Still, there were more than 18,000 new local infections in the seven days through Aug. 18, China’s worst week since mid-May, amid outbreaks in Hainan, Tibet and Xinjiang that stranded tourists and threw the travel plans of thousands of people into disarray.

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The tropical island of Hainan, which is experiencing the country’s worst outbreak since Shanghai’s lockdown in the spring, reported 1,499 cases from 2,018 on Wednesday. More than 100,000 of the 150,000 tourists stranded by the island’s sudden lockdown this month have left, China News reported, though they’ll need to quarantine for three days upon their return home.

China’s Covid czar and a vice premier, Sun Chunlan, is in Hainan to guide Covid control efforts amid tentative signs the situation may be stabilizing. Haikou, the capital, said it would end a 10-day lockdown on Friday if no more infections are found outside of the community for Thursday. The city’s bus routes that don’t pass through high- or medium-risk areas resumed on Friday, though other places remain under widespread restrictions.

Sun’s trip underscores the seriousness of the outbreak in the region, and concern from Beijing about Hainan’s ability to handle the virus. It also highlights fears that people returning from popular vacation destinations and other areas where flareups are occurring could bring the virus with them. 

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That’s been a problem in Tibet, with returning travelers seeding outbreaks in places like Shanghai and Qinghai. Anyone traveling from the region must quarantine, adding further disruption for many tourists. A decision by officials in the southern Yunnan province to deny entry to travelers from Tibet over the weekend because of a lack of quarantine facilities created a four-mile traffic jam involving hundreds of cars, despite police urging residents to avoid the routes that had backed up.

Tibet reported a drop in cases to 680 from 889. Elsewhere, the northwestern Xinjiang region saw its daily cases drop to 256 from 269, while Shanghai detected three cases.

©2022 Bloomberg L.P.