Beijing reported 39 new local confirmed COVID-19 cases between 3 pm on Wednesday and 3 pm on Thursday, bringing the total number of infections to 544 since April 22 across 15 districts, according to the Beijing Center for Disease Prevention and Control on Thursday.

Among the new infections, 38 were reported in controlled zones and one was found during community testing, said Pang Xinghuo, deputy director of the Beijing CDC, at a news conference on Thursday afternoon.

Of the total, Chaoyang district registered 220 cases, the most in the outbreak, followed by Fangshan, which has reported 135.

"The center has completed gene sequencing of virus samples from 220 cases in the latest outbreak," Pang said. "The results showed there are two independent transmission chains in the city."

"The gene sequencing of the virus is identical to the one in the recent clusters outside Beijing, which have spilled out to other parts of the country," she added.

The latest outbreak in Beijing has spread fast, involving a wide range of places. The transmission chains have not yet been completely cut off in the city, as new cases were detected during the mass testing at the community level, Pang said.

Due to the increasing number of COVID-19 cases, four more residential communities - two in Chaoyang and two in Fangshan - were designated as high-risk areas starting Thursday.

As of Thursday afternoon, Beijing had 17 high-risk areas for COVID-19 and 31 medium-risk areas.