Beijing is reintroducing strict lockdown measures and rolling out mass testing after a fresh cluster of novel coronavirus cases emerged from the city's largest wholesale food market, sparking fears of a resurgence of the deadly outbreak.

The Chinese capital reported 36 new Covid-19 cases on Monday, bringing the total number to 79 since a locally transmitted infection was reported on June 12 for the first time in nearly two months, according to the National Health Commission.

The cases are linked to Xinfadi market in the southwest of the city, which supplies most of the capital's fresh fruit and vegetables. The market, which also sells meat and seafood, has been shut down since Saturday.

The outbreak has already spread to the provinces of Liaoning and Hebei, where a total of five new cases were found to be close contacts of patients in Beijing.

The new cluster has sent shock waves throughout China, with Beijing's municipal government spokesman Xu Hejian describing it as “an extraordinary period” during a press conference Sunday.

Chinese state media has repeatedly touted China's effective measures in containing the virus as the number of infections and deaths surged abroad, contrasting its success with the failures of Western governments, especially the United States.

The sudden reemergence of the virus in Beijing, previously considered among the country's safest cities, has raised the prospect of a second wave of infections and the possible reintroduction of the types of sweeping lockdowns that had previously brought much of the country to a halt and hammered the economy.

At a meeting of the State Council, China's cabinet, late on Sunday, Vice Premier Sun Chunlan said the risk of the latest outbreak spreading was “very high,” citing the market's dense and highly mobile population, according to state news agency Xinhua.

“Wartime” measures

Fengtai district, where the Xinfadi market is located, announced Saturday the launch of a “wartime mechanism” and the establishment of a command centre to curb the spread of the virus.

On social media, the Global Times, a nationalist tabloid run by the Chinese government, posted a video of paramilitary police officers donning face masks patrolling the market after it was closed down on Saturday.

Authorities imposed a lockdown on 11 residential compounds in the vicinity of the market, strictly prohibiting anyone from entering or leaving. Residents will have their temperatures checked and reported on a daily basis, and their food and daily necessities delivered.

Beijing also rolled out mass nucleic acid testing for the coronavirus, setting up 193 sampling booths across the city. More than 76,000 people were tested on Sunday, with 59 people testing positive, Xu said at a news conference on Monday.

Nucleic acid tests work by detecting the virus’ genetic code, and can be more effective at detecting an infection, particularly in the early stages, than tests which examine a body's immune response, though the latter are easier to conduct.

Fengtai district has collected samples from 8,950 people who worked in the Xinfadi market. So far, more than 6,000 samples have been tested and the results are all negative, according to Xu.

Authorities also tracked down and collected samples from nearly 30,000 people who had been to the market in the 14 days prior to its closure. All of the 12,000 tests conducted so far showed negative results, Xu said.

The Beijing government has ordered anyone who visited the market and their close contacts to stay home for two weeks for medical observation. It also delayed the resumption of classes for elementary school students, which was originally scheduled for Monday.

Several local officials, including the deputy head of Fengtai district, have been dismissed following the outbreak.

The outbreak is not the first time the virus has returned. In May, several places in the country's northeast were swiftly placed under stringent lockdown after imported cases caused outbreaks among local communities.

Before the new cluster, however, Beijing had only recorded 420 local infections and 9 deaths compared to over 80,000 confirmed cases and 4,634 deaths nationwide, thanks to its strict travel restrictions imposed at the start of the pandemic.

Like much of the rest of the country, life in Beijing had started to return to normal, with businesses and schools reopening, and crowds returning to shopping malls, restaurants and parks.

In a sign of the Chinese government's confidence in its control of the outbreak, the country's parliament even held its annual gathering in late May after a two-month delay, allowing thousands of delegates to travel to Beijing from across the country and sit side by side for meetings that lasted 10 days.

Tracing the source

The outbreak in Beijing will be the latest test of China's coronavirus containment strategy.

Hu Xijin, the editor-in-chief of Global Times, said on Twitter that Beijing will not become the second Wuhan, the original epicentre of the pandemic where the coronavirus was first detected in December last year.

“There is no way Beijing becomes Wuhan 2.0. The world will see China's powerful capacity in controlling the epidemic, including (the) government's strong leadership, respect to science, public's willingness to cooperate and nationwide coordination of control measures. We will win again,” he wrote in a post-Monday.

Beijing authorities are still trying to trace the source of the latest outbreak, however, pledging to conduct “the strictest epidemiological investigations.”

Zhang Yuxi, the market's chairman, told the state-run Beijing News on Friday that the virus had been detected on a chopping board used by a seller of imported salmon at the market, leading to fears of wider contamination. Several supermarket chains have since removed salmon from their shelves, according to Beijing Daily.

While investigations are still underway, a researcher with the Beijing Center for Disease Prevention and Control said genome sequencing indicated the virus found in the market is similar to strains normally found in Europe.

“But it is still uncertain how the virus originated. It could have come from contaminated seafood or meat, or been transmitted by people who have come into the market via their secretions,” Yang Peng, the researcher, told state broadcaster CCTV on Sunday.