The origins of a new cluster of coronavirus infections in Beijing are not certain, World Health Organization officials have said, describing as a "hypothesis" the claim that it might have been caused by imports or packaging of salmon.
Several districts of the Chinese capital put up security checkpoints, closed schools and ordered people to be tested for the coronavirus earlier after an unexpected spike in cases linked to the biggest wholesale food market in Asia.
State-run newspapers reported that the virus was discovered on chopping boards used for imported salmon at Beijing's Xinfadi market amid worries about a second wave of the pandemic in China.
According to the WHO, more than 100 new cases have now been officially recorded in the fresh outbreak in Beijing, with the origin and the extent under investigation.
Mike Ryan, head of the WHO's emergencies programme, said in a briefing that he would be "reticent" to say that packaging needs to be tested for the virus as a result of the new infections.
China races to control fresh outbreak
The outbreak in China, where the disease first emerged last year, had largely been brought under control until a fresh batch of cases was detected in the capital last week.
Health officials reported 49 new coronavirus cases nationwide today, including 36 more in Beijing where a cluster linked to the Xinfadi market has fuelled fears of a second wave of infections.
City official Li Junjie said at a press conference that cases had also been found at the Yuquandong wholesale market in the capital's northwestern Haidian district.
As a result, that market had been closed and nearby schools would be shut, while people living in ten housing estates around it would be forbidden from leaving their homes, he said.
It was not immediately clear how many households were under the new lockdowns, but the orders will affect thousands of people.
The capital has begun mass testing workers from the Xinfadi food market, as well as those who live nearby and anyone who visited it in recent weeks.
AFP reporters saw dozens of people queuing up to be tested at one local stadium this morning, which was heavily guarded by people in hazmat suits.
Officials have said they plan to carry out virus tests on 46,000 residents in the area. More than 10,000 people have been tested already.
Several cities have warned residents not to travel to Beijing.
Authorities are also stepping up efforts to trace people who have visited the Xinfadi market, with companies and neighbourhood communities messaging staff and residents to ask about their recent movements.
At least one building management company asked tenants to declare if any of their staff had visited the market or been in contact with those who had.
The outbreak also turned the spotlight on the safety of Beijing's food chain.
A 19-year-old student told AFP she just started school in the capital a few days ago but plans to return to her hometown because she is worried about the virus.
"I just came to Beijing for a few days. Now I'm going to go home again," she said.
There were also ten imported cases reported, the likes of which have accounted for the majority of China's cases in recent months as overseas nationals return home.
In total, 177 people are now ill with the disease in China, two severely, which is the highest since early May.