Ruili in southwest China's Yunnan Province has closed all roads departing the border city after the emergence of new COVID-19 cases.

The city mayor made the announcement during a COVID-19 prevention and control press conference on Monday, one day after the city logged three locally-transmitted infections.

Authorities have asked local residents to refrain from nonessential travel.

An all-inclusive nucleic acid testing campaign is being launched in the city and the Wanding area, with the government bearing all test-related costs.

Local officials also urged people who left Ruili after June 20 to take a COVID-19 test.