The southwestern China city of Chengdu has been locked down after a spike in COVID-19 cases.
More than 21 million people were been ordered to stay home from 6 p.m. local time on Thursday as part of the city's measure.
While school has been delayed, public transportation is still operating. Approximately 70% of the flights to and from Chengdu have been suspended.
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Residents are permitted to leave the city if they can show a special need.
Just one member of each family who can show a negative virus test within the past 24 hours is allowed outside each day to buy necessities.
Chengdu has reported around 1,000 cases in the latest outbreak, with no deaths. On Wednesday there were 157 domestically transmitted infections.
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The lockdown is the largest since the city of Shanghai was confined for months.
Millions of others were locked down in Dalian and Shijiazhuang.
The nation's stringent "zero-COVID" policy has drawn worldwide criticism, in addition to hurting its economy.
Mainland China has reported no deaths from COVID-19 since May.
It was not clear when the lockdown in the Sichuan Province's capital would be lifted.
Reuters and The Associated Press contributed to this report.
