A senior disease control and prevention official said the two people infected with COVID-19 — found on Tuesday in Guangzhou, Guangdong province — were likely to have caught the virus on a subway, based on an epidemiological investigation.

Zhang Zhoubin, Party secretary of the Guangzhou Center for Disease Control and Prevention, said it is scarcely possible to check and remove all risks and hidden dangers in a short time because of the huge passenger flow on subway trains in the city.

"Gene sequencing indicated the two people, a couple in the city's Yuexiu district, were infected with the Omicron BA.2.76 subvariant that is highly homologous with some previous cases detected in other provinces and regions of the country," Zhang said.

Zhang made the remarks during a news conference on Wednesday.

He urged local residents to strengthen their personal protection and standardize the wearing of masks — replacing them every four hours, or after the masks have become wet, upon arrival in crowded areas or relatively closed spaces.

"Those who come to Guangzhou from outside the city should report to relevant departments, have a nucleic acid test and abide by the city's COVID-19 control and prevention measures to prevent the coronavirus from further spreading in the southern metropolis," Zhang said.

Guangzhou, has a population of about 18 million.

Zhang Yi, deputy director of Guangzhou health commission, said the two infected people, who live on Yuexiu's Lujing Road, have now been sent to a designated hospital for treatment. They have developed mild symptoms.

Their COVID tests came out positive after the couple experienced fevers after returning home from outside Guangdong. They sought help at a nearby hospital on Tuesday morning.

They were confirmed with COVID-19 by a second test later the day, he said.