The 13 million residents of Xi’an were told to remain in their homes and to designate one person to go out every other day for necessities, while non-essential travel out of the city was banned. This came after a second round of mass testing weeded out 127 COVID infections scattered across 14 districts, making containment of the virus “grave and complicated,” the official Xinhua News Agency reported. 

Chinese Vice Premier Sun Chunlan urged “swift” measures to curb the spread of infections, the report said. Sun, whose membership in the 25-person Politburo makes her one of China’s most-senior officials, also stressed the importance of tightening restrictions on the movement of people to prevent large gatherings in key areas, according to Xinhua.

The lockdown of Xi’an is the latest escalation in China’s efforts to extinguish local transmission of the delta variant as it becomes the only country in the world still bent on eliminating the virus and bringing cases to zero. Throughout the pandemic, officials have been able to stamp out outbreaks usually within a month through mass testing, aggressive contact-tracing and targeted lockdowns. Yet as the virus’s new strains become more infectious, containment measures have become increasingly disruptive, putting pressure on the world’s second largest economy.

While local authorities have in the past used targeted lockdowns to slow outbreaks in smaller places in China, no major city has been put under mass restrictions since Wuhan in early 2020, which has a similar population size to Xi’an. 

Meanwhile, China has found four omicron infections from people returning from overseas but has not yet seen the strain, which is far more infectious than delta, spread in the local community. Authorities have vowed to tighten restrictions at borders and ports as they see a mounting risk of infection seeping in from overseas.