Most of the infected people in the latest round of COVID-19 in Guangzhou, Guangdong province, have been asymptomatic carriers or have exhibited mild symptoms, according to a local health official.

Because of the short incubation time for the mutated virus, some close contacts had become positive or had hidden transmission in families and communities during the time they were receiving tests, according to Zhang Yi, spokeswoman for the Guangzhou municipal health commission.

"It has increased the difficulty of prevention and control," Zhang said.

The city reported its highest number of infections on Sunday, with 232 new locally transmitted confirmed cases and 295 asymptomatic carriers, according to the local health authorities on Monday. Most of the cases were found in quarantined and high-risk areas, they said.

In a news conference on Sunday, Zhang said reducing the flow and gathering of people will be key to controlling this new round of the pandemic.

"The virus is constantly mutating and spreading fast, easily causing large-scale outbreaks," she said.

The number of new cases in closed management areas has been trending upward, indicating that there are still people flowing into the areas and causing continuous transmission of the virus, Zhang said.

Temporary measures, including suspension of classes for students, working at home and closure of some businesses have been taken in the city.

"Crowded places, including supermarkets, restaurants and hotels, are seen as distribution centers of the virus," she said. "These are the main cause of the spread."