In response to the outbreak, Tianjin launched a plan on Sunday to test all 14 million city residents by Monday. Tianjin also announced lockdown measures Monday, partitioning the city into three zones with various levels of restrictions.

In the most restrictive areas, residents are barred from leaving their homes under any circumstance. In partial lockdown neighborhoods, one member from each household can leave his or her home to buy groceries every other day. In the least restrictive areas, residents are free to move about in their neighborhoods but not to other parts of the city.

Tianjin authorities also clamped down on the city’s borders, announcing on Monday that residents would need to get permission from their employers or city authorities to leave the city.

“Tianjin’s geographical proximity to Beijing is going to raise concerns about possible outbreaks in the capital, particularly with the Olympics so close,” says Nicholas Thomas, a health governance professor at the City University of Hong Kong. The 2022 Winter Olympics start in Beijing on Feb. 4.

Li Hongzhong, Tianjin’s Communist Party secretary, told local media Monday that Tianjin would act as a “moat” to protect the country’s capital.

But the moat may not have been established fast enough.

On Monday, Anyang, a city in China’s central Henan province, reported two Omicron infections, which authorities traced to two college students who had recently arrived from Tianjin. The cases prompted Anyang authorities to launch their own mass testing scheme to screen the city’s 5 million residents for COVID-19. Meanwhile, Tianjin’s top infectious disease official Zhang Ying said Monday that the disease may have already been spreading in the community well before authorities discovered the cases on Sunday.  

The harsh measures to combat a potential Omicron outbreak in Tianjin come as China’s COVID-zero policy has faced significant backlash in Xi’an, a city of 13 million in China’s central Shaanxi province.

In Xi’an, some residents have been confined to their homes for nearly a month after a Delta outbreak in the city infected 1,959 people starting Dec. 9. But while none of Xi’an’s cases have proved fatal, residents have criticized the government for not providing some areas with access to enough food. Chinese social media users have also condemned local authorities over reports that two women had miscarriages and a man died of a heart attack after hospitals denied them entry owing to COVID-19 policies.

Given Omicron’s increased transmissibility relative to Delta, an Omicron outbreak in Tianjin could push local authorities to adopt even more restrictive policies to contain the highly transmissible variant.

“I think the mainland health authorities will be able to contain Omicron outbreaks, but it may require longer and more stringent lockdowns than previous outbreaks,” says Ben Cowling, an epidemiologist at the University of Hong Kong.