Beijing reported eight clusters of coronavirus infection as of Wednesday, all of which were closely connected with the recently closed Xinfadi wholesale market in Fengtai district.

On Thursday, Beijing reported another 21 confirmed cases of infection in the past 24 hours, said Pang Xinghuo, deputy head of the Beijing Center for Disease Control and Prevention.

At a news conference on Thursday afternoon, Pang provided details about a recent cluster of COVID-19 cases, in which seven infections were detected in people who had gone to the same restaurant and were living in one apartment.

Those seven patients were infected by close contact with people who had been to the Xinfadi market. The food they purchased also originated in the market, Pang said.

"The coronavirus is highly contagious. We should maintain a strong alert in prevention work, wear masks in public places and keep a safe distance with people in public," she said.

The city's public transportation services also imposed traffic controls to prevent the disease from spreading, said Rong Jun, spokesman for the Beijing Commission of Transport on Thursday.

Cross-provincial services of chartered buses and cars, as well as tourism to and from Beijing, have been suspended because of a sharp decline in passengers. People who had purchased tickets can get their money refunded, Rong said.

Also, the commission set load rates for the city's public transportation. For buses, the load rate should be no more than 90 percent and the maximum. For subways it's 80 percent, he said.

On Thursday morning, the city's public security department announced that inspection stations have been set up at the city's highway toll booths, giving departure permission only to those travelers with a recent negative coronavirus test report.

Confirmed cases, suspected cases, close contacts and people with the infection but showing no symptoms will be limited to buying airline or train tickets.