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People queue to undergo nucleic acid testing in the city of Ruili which borders Myanmar in China's southwestern Yunnan province on July 5, 2021. Image Credit: AFP

BEIJING: Parts of a small city in southwest China that shares a border with Myanmar went into a full lockdown on Wednesday as local authorities wrestled with the city’s fourth outbreak of the new coronavirus since the pandemic began.

Residents in the main areas of Ruili, a city in Yunnan province with a population of about 270,000, were told to quarantine themselves at home as schools and businesses shut.

Some markets, hospitals and pharmacies remained open.

Yunnan reported 15 new confirmed locally transmitted coronavirus cases for July 6, with all cases in Ruili. That compares with three cases per day in the city reported for July 4 and July 5.

The Ruili infections will be a test of China’s so-called wall of immunity, with the country’s border regions among the first to get vaccines. Many residents in Ruili have received COVID-19 inoculations, state media have reported.

Two of the cases confirmed for July 6 had previously been identified as asymptomatic cases, which China does not classify as confirmed cases. The other 13 were identified through mass testing in Ruili.

Of the 15 new cases, three were Chinese nationals while the rest were Myanmar citizens, two of whom were children.

So far, seven samples that tested positive for the coronavirus had a genome sequence highly similar to that of the Delta variant and strains from neighbouring countries, Ruili officials said at press conference on Wednesday.

The Ruili outbreak marks the second cluster of infections in China involving the Delta strain, seen by experts to be highly transmissible. The variant was first detected in India.

Ruili is a key transit point for Yunnan, which has struggled to monitor its rugged 4,000km border with Laos, Myanmar and Vietnam for illegal immigration amid unauthorised crossings by those seeking a haven from the pandemic.

“Ruili will continue to strengthen border control measures,” Zhai Yulong, chief of Ruili’s Communist Party, said at the press conference. “We will severely crack down on illegal cross-border activities.” Yunnan province also reported two new locally transmitted asymptomatic cases for July 6 - one a Chinese citizen and the other a Myanmar national.

One new asymptomatic case imported from abroad was also reported, a Chinese national who returned from Myanmar in early June.

The last outbreak of local COVID-19 cases in China was in the southern Guangdong province in May through June, with the Delta variant dominating infections