After the discovery of just three asymptomatic cases, Yuzhou ordered its one million residents to remain indoors and not leave town.

Authorities in Xuchang city, which has jurisdiction over Yuzhou, said in a statement that "the source of the virus is unknown" and "the number of cases is unclear". 

"To curb and quash the epidemic within the shortest amount of time is a high-priority political task facing all officials and people in the city," they said.

Authorities banned vehicles from Yuzhou's roads unless they had clearance, and restricted shopping to only  essential supplies. 

The lockdowns in Yuzhou and Xi'an come at a particularly sensitive time, as China prepares to hold the Beijing Winter Olympics, which open February 4.

'Difficult to buy food online'

Stringent measures to stem outbreaks are common in China, which still maintains a policy of stamping out every COVID-19 case long after many other countries have opted to try to live with the virus.

The Chinese people have largely complied with the tough measures throughout the pandemic, but complaints have cropped up over tough policies, despite the risk of retaliation from Communist authorities. 

"Can't leave the building, and it's getting more and more difficult to buy food online," said one resident of Xi'an, who posted on the social media platform Weibo under the name Mu Qingyuani Sayno.

Authorities in Xi'an had assured the 13 million people largely confined to their homes that they would be able to provide necessities.

Zhang Canyou, an expert with the state council's epidemic prevention and control team, conceded that "there may be supply pressure in communities".

But he was quoted by the official Xinhua news agency saying residents would be looked after.

"The government will go all-out to coordinate resources to provide people with daily necessities and medical services," he said. 

Xi'an's lockdown originally allowed people to leave the house every two days to shop for basic goods, but it has since been tightened, with rules varying in each district, according to the severity of the outbreak.

Some people are not allowed to go out at all and must have goods delivered to them.

In recent days, people in Xi'an could be seen shopping at pop-up markets, served by workers in head-to-toe white protective suits.

Community volunteers also visited people's homes to ask what they needed.

Strain beginning to show:

Residents in Xi'an are increasingly complaining on Weibo about being unable to source necessities.

In one widely shared video, guards could be seen attacking a man who had tried to deliver steamed buns to family members.

The guards later apologised to the man and were each fined 200 yuan ($44), according to a Xi'an police statement posted on Weibo.

China's "Zero tolerance" strategy of quarantining every case, mass testing and trying to block new infections from abroad helped it to contain previous outbreaks.

However, the lockdowns are far more stringent than anything seen in the West, and they have exacted a tremendous toll on the economy and the lives of millions of people.

Sources | AP / Reuters