China has placed as many as 13 million people under lockdown in the northern city of Xi’an after a sharp rise in coronavirus cases.
The country is trying to contain outbreaks of Covid-19 before it hosts the Winter Olympic Games beginning on February 4.
Xi’an city officials have suspended almost all transport to and from the city.
They said all residents should stay at home unless they have a pressing reason to go out.
One person from each household will be permitted to leave home every two days to buy household necessities, the order said.
It took effect at midnight on Wednesday.
There was no word on whether the outbreak was caused by the newly surging Omicron variant or by Delta.
China has reported only seven Omicron cases. Four were in Guangzhou and two in Changsha, both in the south. One occurred in the northern port of Tianjin.
Social media posts recorded panic buying of groceries and household products in Xi’an. The government said more supplies would be brought in.
Residents posting on Thursday said the situation remained relatively calm, with people allowed to travel in and out of the compounds in which they live.
On Thursday, Xi’an reported another 63 locally transmitted cases over the previous 24 hours, pushing the city’s total to at least 211 over the past week. The city is the capital of Shaanxi province, a major centre of industry also famed for its imperial relics.
China has also been dealing with a substantial outbreak in several cities in the eastern province of Zhejiang, near Shanghai, although the targets of isolation measures there have been more narrow.
The country has adopted strict pandemic control measures under its policy of seeking to drive new transmissions to zero, leading to frequent lockdowns, universal masking and mass testing.
Those measures have been stepped up in recent days as the Beijing Winter Olympic Games approach.
The Xi’an restrictions are some of the harshest since China in 2020 imposed a strict lockdown on more than 11 million people in and around the central city of Wuhan, where the coronavirus was first detected in late 2019.
China has reported 4,636 deaths among a total of 100,644 cases of Covid-19.