While the dozens of new cases in Beijing seem slight compared to the hundreds and even thousands of infections reported daily in other countries, the fresh outbreak has jolted China, prompting the government to fire local officials and reinstate some recently relaxed restrictions. The resurgence of cases points to the challenges that governments around the world face as they reopen economies while the virus persists.

“We feel this is dangerous,” Chen Xiaoxi, the owner of a shop about two miles from a market linked to the new outbreak, said by telephone. He said he was waiting for the results of a nucleic acid test to check if he had the virus. “It is a worry; everyone is worried. This is no ordinary disease. We’re waiting at home and can’t go out.”

The city government said on Monday it had tracked down 79 coronavirus infections over the previous four days, including 36 confirmed on Sunday. Virtually all appeared ultimately traceable to the vast, bustling Xinfadi food market in the south of Beijing.