Faced with a rapidly spreading coronavirus outbreak, China is implementing a wave of travel restrictions and quarantine orders, the scale of which has not been seen since the country’s initial explosion of cases from Wuhan last year. Driven by the contagious delta variant, the outbreak will be a closely watched test of China’s vaccines as well as its draconian containment strategy, which until this point has been largely effective in keeping infections low, experts say.

The number of new reported cases is still in the hundreds, but epidemiologists have expressed concern that local clusters have emerged in almost 30 cities, including Beijing, Wuhan, and the flood-hit city of Zhengzhou. Officials have responded swiftly with new restrictions, increased surveillance and, in some places, cash incentives to report on people suspected of carrying the virus. Wuhan has started testing all 11 million residents after seven new cases; Zhengzhou, still reeling from a heavy downpour that killed at least 300, has also begun mass testing.

On Tuesday, the surveillance app used by the government to track people’s travel history and exposure status briefly crashed due to overwhelming traffic. “With the transmissibility of the delta variant, the method of tracing and containing is becoming increasingly difficult,” said Nikolaus Osterrieder, dean of the Jockey Club College of Veterinary Medicine and Life Sciences in Hong Kong. “Like everyone, China is now in a race.”

There’s much at stake for the country’s leaders, not just in terms of public health, but political image, said Yanzhong Huang, a senior fellow for global health at the Council on Foreign Relations. If infections skyrocket, “it is going to not only lead people to question the effectiveness of the existing pandemic control approach but also significantly undermine the official narrative that touts the superiority of China’s political system in handing the pandemic,” he said.

Huang added that the delta outbreak also makes it increasingly unlikely that China will significantly loosen borders in time for the 2022 Winter Olympics in Beijing in February.

Most epidemiologists agree that a zero-tolerance approach is not tenable in the long run, but in the absence of herd immunity, Osterrieder said, Chinese officials does not have many short-term alternatives. More than half of the population had been fully vaccinated as of July, still short of the 80 to 85 percent target that experts say is needed to protect the population.

As of this week, all provinces in China have issued travel warnings or banned nonessential trips to areas considered high risk. Some villages have blocked road access to keep out unwanted visitors, and universities have ordered students and staff not to leave campus. Wuhan University told students to suspend or cancel plans for summer internships unless they were able to move them online.

In Beijing, where more than 80 percent of residents have been vaccinated, most districts have gone more than a year without new cases, government data shows. But in the past week, five new infections have been reported, prompting officials to bar residents from more than a hundred high- or medium-risk areas from entering the city.