Residents in the Anzhenli neighborhood in Chaoyang district were sealed off on Saturday, and will not be allowed to leave their compound.
Beijing is on high alert as it prepares to host the Olympic Games opening on Friday.
While the cases are low compared to other countries in the region, China has doubled down on its “zero-tolerance” policy, which includes breaking the chain of transmission as soon as it is found.
The city is also setting up 19 points in the area to test residents every day until Friday, officials said at a briefing on the pandemic, according to state-backed Beijing News.
The Chinese capital reported a total of 12 cases of COVID-19 between 4 p.m. Saturday and 4 p.m. Sunday, said Pang Xinghuo, the vice head of the Beijing Center for Disease Prevention and Control. All those cases came from people who were already under some kind of pandemic control measures.
The city conducted multiple rounds of testing for millions of residents this past week in Fengtai district, where some residential compounds were locked down.