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.

Wuhan will test all 12 million residents for the coronavirus, an official said on Aug. 3, after the city confirmed its first cases of the Delta variant. (Reuters)

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 of its 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 because of 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 also 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 handling the pandemic,” he said.

Huang added that the delta variant 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 do not have many short-term alternatives. More than half 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.

The capital needs to be “guarded at all costs,” Beijing Communist Party Secretary Cai Qi said in a meeting Sunday where officials decided on the new restrictions. “From top to bottom, the city needs to be on alert,” he added.

The delta variant outbreak began in the eastern city of Nanjing, where officials say workers at Lukou International Airport were probably exposed to the virus by infected travelers from Russia. In 10 days, the virus made its way to at least two dozen other cities, forming new hot spots.

The tourist city of Zhangjiajie, known for its quartz-sandstone pillars and glass skywalk bridge, was placed in lockdown after recent travelers tested positive. Officials say they are racing to track down more than 2,000 people who attended a packed theater performance in late July before scattering across the country.

“I’m not too worried about the Nanjing outbreak, because it is a big city and the containment has been done very well,” Zhong Nanshan, a government-appointed epidemiologist, said Saturday. “But whether the smaller city [of Zhangjiajie] could become a spreader? This we still don’t know.”

Officials are also paying attention to the city of Yangzhou, near Nanjing in Jiangsu province, which has reported 94 new cases since the weekend. Forty-three of the cases have been traced to mah-jongg and chess rooms, local news reported, which have since been shut down.

Yangzhou officials have offered a $770 cash reward to people who file reports of residents who have recently been to specific mah-jongg rooms or who have come to Yangzhou from high-risk areas. If the individual tests positive, the reward will be doubled, reported a Shanghai-based newspaper.