Chinese health officials have reported 25 new confirmed COVID-19 cases - 22 in Beijing and three in the neighboring province of Hebei.
Authorities said that around 2.3 million people were subjected to tests in efforts to curb the further spread of the virus that led to the shutdown of the country's largest wholesale food market.
China, where the outbreak started in December, had relaxed travel and business restrictions as new cases decreased. But, following the recent rise in infections, surveillance and some other restrictions were reinstated.
Between June 13 and June 19, nearly 2.3 million people were tested at close to 2,100 sampling locations manned by around 7,500 health workers and frontliners, the municipal government disclosed. The country registered 26 new cases on Saturday, based on data by the National Health Commission, Sunday.
The new virus cluster in the capital has elevated worries of a resurgence of the highly contagious disease in China, which had generally kept the virus at bay in the past few weeks.
Dozens of areas have been placed under lockdown to control the spread, with residents being told to avoid non-essential travel and schools closed. The new cases of coronavirus infections on Sunday include a nurse - the first medical staff to have been diagnosed with COVID-19 since the re-emergence of the virus just more than one week ago.
Since June 13, people working in the Xinfadi market from which many new coronavirus cases were linked, residents in adjacent communities, and those who visited the market have been called for the nucleic acid tests.
More than 100,000 employees at 17 delivery companies in the capital were estimated to take nucleic acid tests between Friday-Monday, but as of Saturday no one had been confirmed to be infected by the virus, the State Post Bureau disclosed.
Beijing has imposed a policy that makes it mandatory for those who want to leave the city to submit a negative COVID-19 result. Because of this, many residents, who had neither visited the market or lived nearby have listed for testing.
The head epidemiologist of the Center for Disease Control and Prevention told members of the press on Friday that the fresh outbreak had been brought under control but Beijing could still see new cases.
Those who have not visited the Xinfadi market between May 30 and June 12 are at a low risk of getting infected with the virus and don't have to register for the nucleic acid testing, said Liu Xiaofeng, deputy chief of the Beijing CDC.