SHANGHAI: Health authorities in China's southwestern Yunnan province on Thursday reported six new COVID-19 cases in Ruili amid efforts to contain a fresh outbreak in the city bordering Myanmar.

Home quarantine, restrictions on exiting the city, and mass testing started on Wednesday after authorities reported an outbreak of six COVID cases and three asymptomatic patients - those infected but do not show symptoms.

Two of the latest six COVID patients and 10 of the 23 new asymptomatic patients in Ruili are Myanmar citizens, the Health Commission of Yunnan Province said in a statement.

Health authorities in Yunnan have yet to identify how the latest cluster started.

Ruili is a key transit point for Yunnan province, which has struggled to monitor its rugged 4,000 km (2,485-mile) border with Laos, Myanmar and Vietnam for illegal immigration amid a wave of unauthorised crossings last year by those seeking a haven from the COVID-19 pandemic.

Ruili rolled out similar COVID-19 curbs last year after imported infections from Myanmar were detected.

For all of mainland China, a total of 16 COVID cases and 42 asymptomatic cases were reported on March 31, the National Health Commission (NHC) said in a separate statement on Thursday. The Ruili cases accounted for all of the new locally transmitted infections reported by the NHC.

COVID-19 first emerged in the central Chinese city of Wuhan in late 2019 and brought the country to a virtual standstill in early 2020 before it took spread globally. The country has since recovered and new infections now stand at a fraction of what it saw at the height of the outbreak in February 2020.

The total number of confirmed COVID-19 cases in mainland China now stands at 90,217, while the death toll remained unchanged at 4,636.