Residents described the atmosphere as tense. Li Ping, who works at a real estate company in Shulan, population 600,000, stocked up on meat, eggs and noodles as she prepared for the lockdown.
“The government’s controls now are very strict,” she said. “As long as we obey and not go out, it will be all right.”
The latest outbreak is concentrated in Jilin, a northeastern province of 27 million people that sits near China’s borders with Russia and North Korea. Jilin has reported a small outbreak of about 130 cases and two deaths, but experts there have warned of the threat of a “big explosion.”
Officials have already mobilized the police and Communist Party groups to make sure residents comply with the lockdown. Tens of thousands of people are being tested for the virus and thousands rounded up into hospitals for quarantine. The central government has signaled its displeasure about the outbreak, dismissing five local officials and sending top leaders to the province to conduct inspections.
The authorities have also imposed a lockdown on parts of Jilin City, a manufacturing base, bringing factories to a standstill and quieting streets. In some areas, residents are allowed to leave their homes only once every two days, and for a maximum of two hours, to shop for groceries. The strictest measures are probably affecting more than 200,000 people in the city.
“We are doing what is necessary to control and prevent the disease, and to isolate those who need to be isolated,” Song Jing, a government worker in Shulan who is helping to organize widespread testing for residents, said by telephone.
The outbreak points to the persistence of the virus in China despite the punishing restrictions imposed to contain it, including a 76-day lockdown in Wuhan, the central city where the virus first emerged in December. The coronavirus has killed at least 4,600 people in China, though that official count is considered an underestimate.
“The possibility of a second wave is clearly there,” said David Hui, the director of the Stanley Ho Center for Emerging Infectious Diseases at the Chinese University of Hong Kong. “China doesn’t want to take any chances.”
In China, the ruling Communist Party’s swift use of heavy-handed lockdown measures in Jilin also shows its resolve to declare victory in what China’s top leader, Xi Jinping, has described as a “people’s war” against the virus.
A meeting of China’s national legislature begins in Beijing on Friday, and Mr. Xi appears eager to project strength in the face of the uncertainty posed by the pandemic.
“They want to articulate confidence, whether they have it or not,” said Steve Tsang, the director of the China Institute at the School of Oriental and African Studies in London. “The key message is that China, under the leadership of Xi Jinping and the Communist Party, has saved the country from Covid-19 while all these Western democratic countries failed.”
Mr. Tsang said the government’s reluctance to abandon sweeping lockdowns in favor of a more targeted approach pointed to the party’s limited options.
“The system is inflexible, and this is the only way they know how to contain it,” he said. “They are simply not willing to take any risks.”
Mr. Xi is under pressure to shore up the economy, which contracted in the first three months of this year for the first time since the 1970s, and which is still suffering amid the global drop in consumer spending.
The coronavirus outbreak in Jilin has unnerved the public in part because the authorities have struggled to trace its origins.
Officials have tied many cases in the northeast to Chinese nationals who had recently returned from Russia. But many of the recent cases involve people who had not traveled outside the country.
One of the first reported clusters in Jilin was traced to a 45-year-old woman in Shulan who washed clothes at a police bureau and had not been abroad recently. Around a dozen other cases were later linked to the woman. Elsewhere, officials found that a man in Jilin City infected with the coronavirus had attended a large wedding in early May, raising fears of a bigger outbreak.
Adding to the difficulties, Chinese medical experts say the virus is displaying slightly different characteristics in Jilin, as well as in other northeastern provinces where cases have recently appeared, including Heilongjiang.
Patients are taking longer than the typical one to two weeks to show symptoms of the illness after being infected, an expert with the National Health Commission, Qiu Haibo, told the state-run broadcaster this week, and they are carrying the virus for a longer period of time.
Chen Ying, a public health researcher at Xi’an Jiaotong-Liverpool University, said officials were reacting forcefully in the northeast because the experience in Wuhan had demonstrated the importance of early, stringent action.
“If we had this chance in Wuhan, we would have taken similar measures,” he said. “The consequences will be very big if this is not controlled.”
Albee Zhang contributed research.