Health authorities in several cities with new local COVID-19 infections urged residents to stay vigilant and reiterated the use of personal hygiene and protection measures, including wearing masks, maintaining social distancing and paying attention to food safety.

In recent days, three new confirmed cases have been reportedin Tianjin, Shanghai and Fuyang, Anhui province－but authorities reacted quickly with prevention and control measures, officials said.

In Tianjin, large-scale nucleic acid testing started on Monday evening on 77,000 residents of the Hangu subdistrict and the two blocks neighboring a cold-chain logistics area at the central fishing port in the city's Binhai New Area.

The areas were classified as medium-risk for COVID-19 on Tuesday after a 38-year-old man, who works at a loading dock of a cold storage company, tested positive, becoming a confirmed COVID-19 patient on Sunday.

"The tests, progressing around the clock, have gone smoothly," said Li Haiyan, Party secretary of Hangu's Dongbinli community, home to 3,000 people.

Officials also urged residents in the medium-risk areas not to leave their communities.

The novel coronavirus found to have infected the Tianjin patient was very similar to the strain that spread in North America between March and June, local government officials said.

The man tested positive after he handled a shipment of frozen pork last week. Samples of the outer packaging of the pork, which arrived in Tianjin on Oct 19 from Germany, tested positive for coronavirus on Saturday.

On Tuesday, the city reported an asymptomatic COVID-19 case－a 48-year-old man who is a stevedore at Tianjin Dongjiang Free Trade Port Zone in the Binhai New Area.

Also, a second man, 47, a driver who went to the facilities where the confirmed patient worked and who loaded frozen food on Thursday, was reported as an asymptomatic case on Monday.

In Yunnan province, Gengma Dai and Va autonomous county reported two new asymptomatic COVID-19 cases on Monday. The individuals are from Myanmar. An imported asymptomatic case from Myanmar was also reported in Ruili, in the province, on Tuesday.

The county initiated emergency preventive actions soon after, and residents in three communities in Mengding town－Baqu, Qingshuihe and Banxing－were required to complete 14 days of home quarantine. Schools in the town were suspended.

Shanghai's government said on Tuesday that all 8,717 people in the city with ties to the confirmed local COVID-19 patient－a 51-year-old man who works as a cargo handler at Shanghai Pudong International Airport－had tested negative for the virus.

Twenty-six people who had close contact with the confirmed patient and 186 people who interacted with those individuals have also been quarantined at designated hotels, according to the authorities.

In Shanghai's Pudong New Area, Yingqian, a village in Zhuqiao where the patient lives, was designated as a medium-risk area for the spread of COVID-19 on Monday.

However, a confirmed COVID-19 case, a close contact of the Shanghai patient, was reported in Fuyang, Anhui province, on Tuesday. The 50-year-old man also worked as a stevedore at Shanghai Pudong International Airport.

Zhou Huiying contributed to this story.