(Bloomberg) -- China placed the 17.5 million residents of the southern city of Shenzhen into a lockdown that’s due to last until March 20, AFP reported, citing a city government notice.

The measures, which came after virus cases doubled nationwide to nearly 3,400, extend restrictions placed earlier on the city’s central business district. The surge in infections is thought to be linked to the neighboring city of Hong Kong, where about 300,000 people are currently in isolation or under home quarantine. Alongside the lockdown, Shenzhen will launch three rounds of mass testing of residents.

All bus and subway systems across the city were ordered to shut during the restrictions. Businesses, except those providing essential services will also close, and employees will work from home if they can. Residents will be barred from leaving the city, except in limited situations, and they will need to produce a negative Covid test within 24 hours, AFP said. 

The growing clusters spawned by the highly infectious omicron variant in China’s most developed large cities and economic powerhouses have turned into an unprecedented challenge for the country’s Covid-Zero strategy, a policy abandoned by the rest of the world. Officials have largely resisted tactics such as lockdowns and mass testing and relied mostly on targeted responses, only to see omicron continue to spread.

Shenzhen is also under pressure to prevent infections from seeping in through Hong Kong, which has seen daily cases rise to tens of thousands. Hong Kong’s health system and morgues have been under pressure from the record outbreak that’s pushed its death rate to one of the highest in the world. While the virus case count in the city has steadily declined over the past week, fatalities have risen. 

The Hong Kong government is still formulating plans for the mandatory testing exercise of all residents, including the timing and how to ensure essential operations can continue if movement restrictions were to be imposed, Lam said Wednesday. For now, authorities will focus on a vaccination drive for elderly people living at care facilities -- which are seeing a surge in fatalities -- and increase the number of hospital beds to treat patients, she said.

Cases are spreading in other parts of the mainland. Shanghai, China’s financial hub, is battling a rising number of omicron infections that have prompted school closures for students from kindergarten through middle school next week. 

The operations of nine cross-province bus stations that mainly offered service to provinces including Jiangsu, Zhejiang, Anhui, Shandong and Jiangxi were halted, according to a statement Sunday on a local government website. Shanghai will suspend all cross-province bus services from March 14. 

Shanghai Disneyland will operate at controlled capacity and will require visitors to present negative Covid test results from within 24 hours of entering the amusement park. 

(Adds lockdown details)

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