Mainland China is struggling to contain its biggest coronavirus outbreak since the pandemic erupted in Wuhan two years ago, as the Omicron variant tests President Xi Jinping’s zero-tolerance strategy and puts Shanghai at risk of being locked down.

Changchun, the capital of northeastern Jilin province with 9mn people and an important manufacturing base, was ordered into lockdown on Friday after 23 new cases were reported, the latest in a series of citywide crackdowns in recent months.

Health authorities reported that daily case numbers have tripled in the past week, adding up to more than 1,100 cases across 17 regions and forcing officials in several cities to erect emergency makeshift hospitals.

The latest rise in China’s cases has refocused attention on Xi’s decision not to stray from its zero-Covid strategy of tightly sealed borders and — whenever an infection is detected — citywide lockdowns, mass testing and meticulous contact tracing.

Speaking to reporters after the close of China’s parliamentary session on Friday, Premier Li Keqiang did not answer questions about how much longer the government intended to stick with its zero-Covid strategy.

“We will continue to make our response more scientific and targeted,” Li said, adding that Beijing remained determined to “protect people’s lives, [maintain] normal work and life, and ensure the security of industrial and supply chains.”

The policy, which has been credited with suppressing China’s pandemic death rate, has endured despite authorities delivering more than 3bn Covid-19 vaccine doses to a population of 1.4bn.

China’s case numbers remain low by almost all international comparisons. New Zealand, a country of 5mn people, reported more than 20,000 new infections on Friday, while South Korea said there were 280,000 cases among its 52mn.

While much of the rest of the world is rapidly reopening, Beijing’s approach reflects shortcomings in China’s healthcare system, said health experts, who pointed to the comparatively low efficacy of the country’s domestically produced vaccines.