All domestic passenger flights to and from the Guangzhou Baiyun International Airport on Friday and Saturday were canceled after some workers at the airport tested positive for COVID-19 during routine testing.

Cargo and international flights will remain as scheduled.

The city of Guangzhou, capital of Guangdong province, reported three confirmed COVID-19 cases and one asymptomatic carrier by noon on Thursday after routine testing organized by the airport management the day before. Three are airport workers and one is a family member of an infected airport worker. Another 11 people tested positive in initial screening, Chen Bin, deputy director of the city's health commission, said at a news conference on Thursday.

After some workers came back with abnormal test results, mass nucleic acid testing was carried out among airport workers starting at 10:30 pm on Wednesday, with 48,819 samples taken by 1 pm the following day, said Huang Hao, deputy general manager of Guangzhou Baiyun International Airport.

For the workers whose results were abnormal, their family members and those who had worked with them in the previous four days were immediately required to quarantine at home.

The two passenger terminals were disinfected starting Wednesday night after samples were taken from the airport environment. Domestic flights, which had all been canceled by noon, began to resume at 2:30 pm. International flights were not affected, Huang said.

For flight safety, related airport staff were placed under closed-loop management, receiving two nucleic acid tests a day for three days. Since May last year, airport staff had been taking three tests a week, with those on key posts taking daily tests in closed-loop management, he said.

By Thursday noon, 79 samples were collected in related environments with all coming back negative, Chen said.

The Airport South metro station was closed on Thursday morning and resumed in the afternoon. Mass nucleic acid testing was carried out in seven districts in Guangzhou on the same day, with 1.42 million samples taken by noon.

For the moment, the outbreak mainly involves airport workers and those living with them. The origin of the infection has yet to be worked out, said Zhang Zhoubin, Party secretary of the Guangzhou disease control and prevention center.

Guangzhou Baiyun International Airport, with an annual passenger throughput exceeding 40.2 million in 2021, is currently China's busiest airport in terms of annual passenger throughput, according to the Civil Aviation Administration of China.