The new cases bring the number of infections confirmed in the Chinese capital over the past five days to 106, as city officials locked down almost 30 communities in the city and tested tens of thousands of people.

Authorities shut down another market on Tuesday -- Tiantaohonglian in the central Xicheng district -- after one employee there was diagnosed with COVID-19, state broadcaster CCTV reported.

Seven residential estates surrounding the market were also locked down.

The World Health Organization said the new cluster was a cause for concern, given Beijing's size and connectivity.

"A cluster like this is a concern and it needs to be investigated and controlled -- and that is exactly what the Chinese authorities are doing," WHO emergencies director Mike Ryan said.

Beijing officials said they will give virus tests to stall owners and managers at all of the city's food markets, restaurants and government agency canteens.

All indoor sports and entertainment venues in the city were ordered to shut on Monday, and some other cities across China warned they would quarantine those arriving from Beijing.

The National Health Commission also reported four new domestic infections in Hebei province, which surrounds Beijing. 

Another case reported in southwestern Sichuan province was linked to the Beijing cluster, health officials said.

Officials had said Sunday that all cases of infection up until then had been linked to the Xinfadi market, which 200,000 people had visited since May 30.

More than 8,000 workers from the market have been tested and sent to centralized quarantine facilities.

Until this recent outbreak, most of the cases in recent months have been Chinese nationals returning home as the pandemic spread to other countries.

China's Center for Disease Control and Prevention said Monday that the virus strain found in the Beijing outbreak was a "major epidemic strain in the European countries".

While the virus was detected on chopping boards used to handle imported salmon at Xinfadi, "it does not clearly or definitely indicate it's from imported seafood", Wu Zunyou, the body's chief epidemiologist, said in a CCTV interview.

"Ever since new cases suddenly emerged in Beijing, we have tried to figure out the reasons for the outbreak since there were no COVID-19 cases found over the past two months," Wu Zunyou said.

"We came up with several possibilities, and the most likely one is that the carrier of the novel coronavirus comes from outside China or other parts of China and brought it here." 

On Tuesday, another eight imported cases were reported.