Residents follow a health worker to a testing station at a sports center in Xicheng district after Beijing municipal government demanded all residents who visited the Xinfadi food market since May 30 to undergo nucleic acid tests for possible infection with the novel coronavirus after the city reported 51 confirmed COVID-19 cases as of Sunday. Photo: Li Hao/GT

The Beijing's COVID-19 outbreak likely began around the end of May and the next three days will be critical and decisive for China's capital to curb the epidemic, a top expert from China's Center for Disease Control and Prevention (CDC) said.

Wu Zunyou, a top epidemiologist with China's CDC, told China's Central Television (CCTV) Monday night that the infection in Beijing's Xinfadi wholesale market was possibly caused by contaminated goods or the transportation process. A Beijing CDC researcher said that the genome sequencing showed that the coronavirus was from a European strain. 

The next three days will be critical for Beijing to curb the outbreak, as people infected with the coronavirus start to show symptoms, he said. 

The earliest cases in Beijing were likely infected with coronavirus near the end of May. 

"The earliest diagnosis was on June 11… We believe that person was infected in late May or early June," Wu said. 

The current epidemic situation in Beijing is still a local event with a very limited scope. It is not necessary to adjust the response level of the entire city. Currently the controls of the Xinfadi wholesale market is robust and "we have confidence that the current outbreak will not spread widely," Wu said.

Beijing has reported 79 COVID-19 active confirmed cases as of press time. The city also reported six asymptomatic carriers on Monday, taking their total number to seven.