Chinese City to Test Nine Million for Coronavirus After Finding a Dozen Cases

Concerns spread Monday on Chinese social media that visitors to Qingdao might have taken the virus home with them. A popular destination known for its beaches and beer, Qingdao handled more than 4.4 million tourist visits over the holiday, according to government statistics.

The Qingdao government said Monday that it had tested close to 280,000 potential contacts as of noon and that it aimed to test everyone in the city within five days.

Chinese authorities remain on high alert for potential Covid-19 outbreaks despite having largely brought the pandemic under control within the country’s borders. On Monday, the National Health Commission dispatched a working group to Qingdao to help with epidemic-prevention efforts, state broadcaster China Central Television reported. Several cities discouraged travel to Qingdao and urged residents who had visited there recently to report to authorities and get tested immediately.

While the daily new-case counts in the U.S. and Europe are in the tens of thousands, China’s are in the low two digits, and almost all the infections are brought in by people traveling from other countries. New arrivals who test positive are immediately placed in strictly enforced quarantine. Those efforts have helped China’s economy bounce back faster than those of major competitors, and officials are eager to prevent a second wave of infections that could derail the recovery.

Chinese health authorities have responded to local outbreaks by putting cities in “wartime mode.” In June, for example, when a batch of cases was discovered in Beijing linked to the Xinfadi food market, the city imposed travel restrictions, locked down nearby residential compounds and mobilized neighborhood groups to conduct temperature checks and enforce quarantines.

Similar responses followed the discovery of new clusters in the country’s northeast, far northwest, and in Wuhan, the central Chinese city where the pandemic began.

Authorities haven’t put Qingdao under lockdown yet, although the local government said it has implemented quarantine measures at the Qingdao Chest Hospital and residential communities where the newly discovered Covid-19 patients lived.

The city, home to China’s best-known brewery, went ahead as planned with its annual three-week beer festival in August, though organizers required participants to wear masks and maintain social distancing. There were no official reports of any Covid-19 cases linked to the event, which drew more than 1.2 million visitors, according to the official Xinhua News Agency.

A trade expo scheduled for later this month in the city was delayed to aid pandemic-prevention efforts, state media reported Monday.

Qingdao hasn’t suffered a major outbreak during the pandemic: Confirmed cases since it began total 65, with one death, according to official figures as of Sunday.

Local governments as far away as Tongliao—a city in Inner Mongolia that is 850 miles from Qingdao by road—issued statements calling on residents to remain alert.

—Xiao Xiao contributed to this article.

Write to Chao Deng at Chao.Deng@wsj.com