The city of Xian in northwest China’s Shaanxi province with some 13 million residents went into a lockdown on Thursday following the detection of 234 Covid-19 cases since December 9.

All residents have been ordered to stay indoors, communities have been put under “closed management”, and outgoing transport including trains and flights have been cancelled, health authorities said on Thursday as the city started the third round of nucleic acid testing for all residents.

Thousands of contacts have been moved to centralized quarantine and put under observation.

Starting Thursday, only one family member of each household is allowed to leave the house to purchase daily necessities every two days, city health authorities said.

The city, known for the Terracotta Army historical site, has suspended long-distance bus services and banned taxis and cars hired on ride-hailing platforms for trips out of town.

The number of confirmed coronavirus cases at 234 is low for a big city but given China’s “zero-Covid” policy, the lockdown is likely to be strictly implemented.

City authorities directed movie theatres to suspend operations and prohibited dining in at restaurants; large-scale events have been banned and schools have either shut or moved classes online.

Yang Zhanqiu, a deputy director of the pathogen biology department at Wuhan University, told the tabloid Global Times the key reason for the lockdown “lies in the scale of community transmission in Xian and unclear epidemiological routes – the outbreak has demonstrated at least three transmission chains”.

No infection caused by the Omicron variant has been detected in Xian.

The local outbreak, according to the tabloid, has spilled over to at least four other cities, including Yanan and Xianyang in Shaanxi province, Dongguan in south China’s Guangdong province, and Beijing.

The Chinese mainland on Wednesday reported 71 new locally transmitted Covid-19 cases, the national health commission said in its daily report on Thursday.

Of the new local cases, 63 were reported in Shaanxi, four in Guangxi, two in Henan, and one each in Zhejiang and Guangdong, the commission said.

As many as 29 new imported cases in nine provincial-level regions were detected, according to the commission.

The total number of confirmed Covid-19 cases on the mainland had reached 100,644 by Wednesday, including 1,823 patients still receiving treatment, of whom 10 were in severe conditions, official news agency Xinhua reported, adding that the death toll remains at 4,636.