China has announced a lockdown for the 21.2 million residents of Chengdu, one of its largest cities, as authorities battle a new COVID-19 outbreak.

The Chengdu city government is launching four days of mass COVID-19 testing and asked residents to "stay home in principle" from 6 p.m. on Thursday, according to an official announcement.

The government added that each family would be allowed one person to go out and procure essential items. Residents were asked not to leave the city unless absolutely necessary. It did not specify how long the lockdown would last.

"The current state of epidemic control is abnormal, complex and grim," the announcement said. It added that the aim is to "decisively arrest the spread of the outbreak and guarantee the health of all citizens."

The government said Chengdu, the capital of Sichuan province, had recorded 157 new local infections on Thursday.

According to data from Flight Master, the number of planes to and from Chengdu has been greatly reduced.

China's zero-COVID policy

China has relied heavily on its zero-COVID policy despite concerns the approach is smothering its economic recovery from the pandemic. 

The policy has severely dampened economic activity as tens of millions of people are stuck at home, while the nation's borders are also mostly shut to international visitors.

Other major cities, including Shenzhen in the south and Dalian in the northeast, also announced COVID restrictions this week.

The restrictions include work-from-home requirements, online learning for schools and the closure of entertainment businesses.

Earlier this year, Shanghai was under strict lockdown for two months.

ss/wd (Reuters, AFP)