Beijing reported 21 new locally transmitted COVID-19 cases between 4 pm Saturday and 4 pm Sunday, including 16 confirmed patients and five asymptomatic cases in Chaoyang, Shunyi and Fangshan districts, bringing the cumulative total to 41 since Friday, senior officials said on Sunday.

This round of cases involved students, teachers, a tour group for seniors, interior decoration staff and delivery workers for restaurants.

The infected have visited several places according to Pang Xinghuo, deputy director of the Beijing Center for Disease Control and Prevention. Among the 41 cases, around one quarter of the total are 60 years old or above. Half of those had not been vaccinated.

"The center has done the gene sequencing of four samples from the infected for this cluster and the result showed the Omicron variant," Pang said at a news conference on Sunday afternoon.

The virus gene sequencing is identical to the recent infection cluster outside Beijing, she said.

"The epidemiological investigation of the case who participated in a tour of the city is still going on and the source needs to be defined."

She said preliminary epidemiological investigation showed the virus has been spreading insidiously for one week already, which has created difficulties for virus control and prevention.

All the districts involved have taken rapid control measures as well as steps to ensure people's daily supplies in the controlled areas.

Pang announced one residential community in Chaoyang is listed as a high-risk area and another one became a medium-risk area starting Sunday. All other areas of the city are low-risk.

Yang Beibei, deputy head of Chaoyang district, said starting Monday the district will conduct nucleic acid tests for all residents.

"People in Chaoyang should try to reduce social activities," she said. "All sports, art and training schools in the district have suspended offline classes since Saturday."