China has released genome data for the coronavirus found in a new outbreak in Beijing, which state experts suggest share similarities to European strains, as the number of cases neared 200 on Friday.
Tens of thousands of people in the Chinese capital are being tested for the contagion while neighbourhoods have been locked down and schools closed as authorities seek to contain a cluster linked to the Xinfadi food market.
Another 25 cases were confirmed in Beijing, taking the total number of infections since last week to 183.
On Thursday Chinese authorities shared the genome data of the latest outbreak with the World Health Organization and international scientific community.
Initial findings suggest it "came from Europe", but is different from what is currently spreading there, said Zhang Yong of the Chinese Center for Disease Control and Prevention (CDC).
"It is older than the virus currently circulating in Europe," Zhang said in a report published by the Communist Party's anti-corruption watchdog on Friday.
Zhang raised the possibility of the virus lurking in imported frozen food or in the wholesale market itself, resulting in similarities to older strains.
The virus had been detected on chopping boards used to handle imported salmon at the market.
But scientists cautioned against making early conclusions on the Beijing cluster.
Ben Cowling, a professor at the University of Hong Kong's School of Public Health, told AFP "it is possible that the virus now causing an outbreak in Beijing had travelled from Wuhan to Europe and now back to China."
But he said the first case has not yet been identified and it may be too late to find out how this outbreak started.
Francois Balloux of University College London wrote on Twitter that -- based on the data shared -- there had been local transmission for some time before the outbreak was identified.
"Their position in the tree does not allow to confidently assign a geographic origin to the lineage. They could have originated from essentially anywhere," he wrote.
Xinfadi supplies more than 70 percent of Beijing's fresh produce and has been temporarily closed due to the cluster.
Wu Zunyou, chief epidemiology expert at the CDC, had previously said the virus found in Beijing was similar to European strains -- although he added this did not mean the virus had been directly imported.
The resurgence came after China had largely brought the virus under control and eased restrictions on movement inside the country.
There are now 293 people ill with COVID-19 in China, the highest number since early May.
Until recently most new cases had been imported by nationals returning from abroad.