Beijing's airports cancelled two-thirds of all flights on Wednesday and schools in the Chinese capital were closed again as authorities rushed to contain a new coronavirus outbreak and warned infections may rise.
The city reported 31 new cases while officials urged residents not to leave Beijing, with fears growing about a second wave of infections in China, which had largely brought the contagion under control since its emergence in Wuhan late last year.
Hundreds of thousands of people have been tested so far following the fresh outbreak, which is believed to have started in the sprawling Xinfadi wholesale food market.
Almost 30 residential compounds in the city are now under lockdown.
"Because the Xinfadi market is the largest marketplace selling daily necessities, with thousands of migrant workers and a large number of visitors, it is hard to control the spread," said Pang Xinghuo, deputy director of the Beijing Center for Disease Control and Prevention.
"We may see a rise in confirmed cases in the coming days," Pang told a regular press briefing.
Beijing has reported 137 infections over the past six days and 95 percent of them were "mild cases", Pang said.
The city has ramped up its testing capacity and is gathering about 400,000 samples a day, said Zhang Qiang, an official from Beijing's epidemic prevention task force.
Since June 13, 356,000 samples have been tested. That includes swabs from workers and visitors to different markets in Beijing and communities near to spots where outbreaks have been registered.
A shortage of expensive testing machines has led to delays in processing.
At least 1,255 scheduled flights were cancelled Wednesday, state-run People's Daily reported -- nearly 70 percent of all trips to and from Beijing's main airports.
The outbreak had already forced authorities to announce a travel ban for residents of "medium- or high-risk" areas of the city, while requiring all other residents to take nucleic acid tests in order to leave Beijing.
Several provinces were quarantining travellers from Beijing, where all schools -- which had mostly reopened -- have been ordered to close again and return to online classes.
- Markets closed -
Officials have closed 11 markets and disinfected thousands of food and beverage businesses in Beijing after the outbreak was detected.
In addition to the cluster in Beijing, two domestic cases -- one in neighbouring Hebei province and another in the eastern province of Zhejiang -- were reported Wednesday, while there were 11 imported cases.
A local case was also reported in Tianjin, a large city located just outside Beijing to the southeast, state television announced late in the day.
The 22-year-old man, a hotel restaurant worker, reportedly had not left Tianjin in the two weeks before displaying symptoms -- fueling speculation about another possible cluster.
Authorities have so far banned group sports, ordered people to wear masks in crowded enclosed spaces, and suspended inter-provincial group tours in response to the outbreak.
Bars in Beijing's trendy Sanlitun area were ordered to shut down, while shops were seeing lighter foot traffic.
Officials said that since May 30, more than 200,000 people had visited Xinfadi market, which supplies more than 70 percent of Beijing's fruit and vegetables.
Until the new outbreak, most of China's recent cases were nationals returning from abroad as COVID-19 spread globally, and the government had all but declared victory against the disease.
China's Center for Disease Control and Prevention said Monday that the virus type found in the Beijing outbreak was a "major epidemic strain" in Europe.