Chinese health officials reported 49 new coronavirus cases on Monday, including 36 more in the capital Beijing where a fresh cluster linked to a wholesale food market has fuelled fears of a second wave of infections.
The domestic outbreak in China — where the disease first emerged last year — had largely been brought under control but then a fresh batch of cases was detected in the capital last week.
In addition to the new Beijing cases, the National Health Commission said there were three confirmed cases in Hebei province, which surrounds Beijing.
Beijing has begun mass testing workers at the Xinfadi food market, as well as those who live nearby and anyone who visited it in recent weeks.
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.
Eleven residential neighbourhoods near the market have been put under lockdown, and several cities have warned residents not to travel to Beijing.
Authorities are also stepping up efforts to trace those who have visited the market, with companies and neighbourhood communities messaging staff and residents to ask about their recent movements.
There were also 10 imported cases on Monday, 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.
There were also 18 new asymptomatic cases, of which seven were domestic. China is not counting asymptomatic cases as confirmed ones.