A fast-spreading variant known as “stealth omicron” is testing China’s zero tolerance strategywhich had kept the virus at bay since the initial deadly outbreak in the city of Wuhan in early 2020. While the numbers are low compared to elsewhere in the world, the more than 10,000 cases recorded by China in the past first two weeks of March far exceed earlier surges.

No new deaths have been reported in the multiple outbreaks across China. Most of the new cases have been in northeast China’s Jilin province, where 2,601 have been reported. Smaller outbreaks have affected more than a dozen provinces and major cities, including Beijing, Shanghai and Shenzhen.

Jilin has banned residents from leaving the province and traveling between cities within it. The 9 million people of Changchun, the provincial capital and an auto manufacturing hub, have been locked down since Friday as authorities carry out repeated rounds of mass testing both there and in the city of Jilin.

More than 1,000 medical workers were airlifted from other provinces with pandemic response supplies, and the province mobilized 7,000 military reservists to help with the response.

Elsewhere in China, Shandong province had the most new cases with 106. Southeast Guangdong province, where the metropolis and major tech hub of Shenzhen have been confined since Sunday, reported 48 new cases . Shanghai had nine and Beijing reported six.