China’s commitment to a zero-tolerance approach for coronavirus infections may be starting to fray.

Since the start of the pandemic, China has embraced a stringent approach to containing the coronavirus, sealing off entire cities and tightly controlling borders to keep infection rates down.

Officials borrowed from the same playbook when a cluster of cases recently emerged in the eastern city of Nanjing, placing 9.3 million residents in semi-lockdown. Nearly all in-person commercial and social activity was suspended and neighborhoods considered high-risk were cordoned off. Taxis were told not to leave the city, and residents were subject to mass testing.

But as coronavirus cases continued to pop up this week in other cities as a result of the highly contagious delta variant, driving new infections in China to a six-month high, some experts have suggested the need for a shift in strategy.

“The Nanjing outbreak has prompted a national stress test and serves as food for thought for the future of our pandemic response,” said Zhang Wenhong, an infectious-disease specialist often regarded as China’s Anthony S. Fauci, in a statement Thursday.

He warned that if the outbreak, which has been linked to 177 cases as of Thursday, worsens significantly, “more decisive measures may be needed.” And he urged people to continue strictly adhering to precautions like mask-wearing and staying at home. But in a break from China’s official tack, Zhang also acknowledged that the country needs eventually to learn how to live with the virus.

“Whether we like it or not, there will always be risks ahead,” he said. “Every country is figuring out their own answers for how to live with the virus. China once produced a beautiful answer sheet, and after the Nanjing outbreak, we will have more to learn.”

Governments across the world have been wrestling with how to balance reopening with the delta variant, which can severely sicken the unvaccinated and be transmitted even among the vaccinated.

Parts of Europe have reopened to vaccinated travelers but reinstated domestic restrictions. Singapore said it would be shifting into a new pandemic normal, then sharply changed course when infections erupted at karaoke lounges and a large fishery port.

In China, whose leaders have repeatedly touted the superiority of its zero-tolerance approach at home and abroad, leaders have found themselves in a growing dilemma of how to move forward. More than half of China’s population has been fully vaccinated, although the country’s top epidemiologist said it will take at least 80 percent to reach herd immunity.

“I don’t think China is going to change its zero-tolerance approach. They’ve always set zero as their goal,” said Dong-Yan Jin, a virologist at the University of Hong Kong. Some countries are trying to evolve away from zero-tolerance, he said, citing Singapore, but it’s not clear whether China can safely do so given questions about the efficacy of its main vaccines, from Sinopharm and Sinovac.

And yet, it doesn’t seem like China’s existing strategies are sustainable, said Yanzhong Huang, a senior fellow for global health at the Council on Foreign Relations. “What is interesting about Nanjing is that it clearly shows that with the delta variant, China’s playbook has diminishing returns,” he said.

The outbreak started in Nanjing’s Lukou International Airport, where the vast majority of employees are vaccinated, local officials said. Cases linked to Lukou have been detected in at least 13 cities in seven provinces, although according to officials, only a handful of those cases have been severe. No deaths have been reported.

Huang said there is a growing set of public health experts and policy scholars that is beginning to question the wisdom of the government’s draconian approach, and some people have said for months that having zero infections in a country as large as China is unrealistic.

But after a year of decrying the more liberal approach taken by the United States as “immoral,” “irresponsible” and “unacceptable,” Chinese political leaders face a dilemma.

“If you basically abandon the zero-tolerance strategy … you need an explanation for why you decided to trash that other approach,” Huang said. “It’s now more a political than a public health consideration.”

He added that, in enforcing its pandemic approach, China’s leaders have created a system that is rather “sticky.” Unlike in the United States, where local and state officials have largely taken charge of pandemic restrictions — causing an ever-changing patchwork of different policies — city and provincial bureaucrats in China have operated primarily on a central set of guidelines from which they aren’t likely to stray in the near future.

The commitment to zero-tolerance is strong even among some residents, who have come to associate it with a sense of safety, Huang said.

Since Nanjing was placed into a semi-lockdown, some users on the microblogging site Weibo have expressed frustration with the new rules, but even more have scolded the government for not taking more dramatic action.

“Why aren’t they sealing off the city!!!” one user ranted on Wednesday as reports rolled in of new infections. “I really don’t understand what the Nanjing government is doing.”

Lyric Li contributed to this report.