Beijing is facing the most complicated and severe epidemic control and prevention situation since the start of the COVID-19 pandemic in 2020, with the number of infections in the city continuing to rise at a high level, a senior official said on Monday.

"The omicron variant BF.7 has become the main strain in Beijing, with the characteristics of being extremely infectious and easily concealed," Liu Xiaofeng, deputy director of the Beijing Center for Disease Prevention and Control, said at a news conference on Monday.

Between Friday and Sunday, cases were mainly reported in Chaoyang, Changping, Haidian, Fengtai and Tongzhou districts, involving 241 subdistricts and villages, he said.

Between midnight and 3 pm on Monday, Beijing reported 316 locally transmitted COVID-19 infections, with 280 of them asymptomatic carriers. Among them, 274 were found in those under quarantine and the remaining 42 were detected at the community level.

Chaoyang, the hardest-hit district during the ongoing outbreak in the capital, reported 146 cases during the same period, among whom 12 were found at community level.

"Residents of the district are still being advised not to leave the area unless necessary," Yang Beibei, deputy head of Chaoyang, said on Monday. "The number of cases in Chaoyang is still rising with an obvious upward trend."

In order to discover and cope with the epidemic as early as possible, starting on Tuesday the city government will require all people returning to the capital to take nucleic acid tests once per day for three successive days, announced Xu Hejian, spokesman of the municipality, at a news conference on Monday.

"People should stay at home until the first negative result of the tests comes out," he added. "The ones who fail to take three tests in three days after arrival will receive an alert via their Beijing Jiankangbao, or Health Kit."

Beijing reported 154 local confirmed cases and 808 asymptomatic carriers on Sunday in total, according to the city's health commission on Monday morning.

The commission also reported two COVID-19 deaths, in addition to one death already reported on the previous day.

The two new deaths — aged 91 and 88 — both had underlying issues such as high blood pressure and cerebral infarction. They died on Sunday.

Other cities with mass infections have adopted strengthened measures to cut the spread of the virus.

Shijiazhuang in Hebei recorded two local confirmed cases and 639 asymptomatic carriers on Sunday, according to the provincial health commission.

Since Monday, the city has started mass nucleic acid testing in six of its districts including Qiaoxi and Chang'an, which will last for five consecutive days till Friday.

Residents in these six districts have been told to work from home, according to a notice released on Sunday night by the city's anti-epidemic work group.

According to the notice, only one member from a household is allowed to go out for a maximum of two hours to buy supplies each day, with a negative nucleic acid test result taken within 24 hours.

Public places including restaurants and shopping malls have been closed.

Primary and secondary schools as well as kindergartens will hold online classes, while colleges and universities are under static management.