XI'AN: Over 13 million people were ordered to stay home in the Chinese city of Xi'an, which imposed a strict lockdown on Wednesday and dramatically tightened travel controls to fight a growing COVID-19 outbreak.

With Beijing preparing to host the 2022 Winter Olympics in February, China is on high alert as it fights local outbreaks in several cities.

The new restrictions were imposed after Xi'an reported 52 new coronavirus cases on Wednesday, bringing the total to 143 since December 9.

From midnight on Thursday, all households may only "send one household member outside once every two days to purchase necessities," with all others ordered to remain indoors except for emergencies, the city government said in a statement on its official Weibo social media account.

Residents "should not leave the city unless necessary," the government said, adding that those seeking to leave would have to provide evidence of "special circumstances" and apply for approval.

The orders came a day after the city in northern China began testing all of its 13 million residents.

Long-distance bus stations were closed and authorities have set up disease control checkpoints on highways out of Xi'an, government notices said.

More than 85 percent of flights to and from the city's main airport have been grounded, according to flight tracker VariFlight.

Inside the city, passenger capacity has been slashed on public transport and schools closed.

All "non-essential" businesses and public facilities aside from supermarkets, convenience stores and medical institutions have been ordered to close, while the local government has urged employers to allow people to work from home, CCTV had reported.

Large-scale meetings including activities in outdoor parks have been suspended, while the museum housing the world-famous Terracotta Army -- the 2,000-year-old mausoleum of China's first emperor -- has shut until further notice.

- Zero Covid -

China -- where the coronavirus was first detected -- has slowed new cases to a trickle since the middle of last year through a zero-Covid strategy involving tight border restrictions, targeted lockdowns and lengthy quarantines.

Even a single case can lead to a swift imposition of curbs.

The southern city of Dongxing on Tuesday ordered its 200,000 residents to isolate at home after an infection was detected.

The country has stepped up its already-strict zero-tolerance Covid policy as it braces for the arrival of thousands of international athletes at the Olympics just over a month away, with the capital Beijing demanding negative Covid tests from visitors and limiting flights from other cities.

COVID-19 is not the only scourge to hit Xi'an in recent weeks, with the city also logging several cases of potentially deadly haemorrhagic fever since the beginning of winter.

Local authorities have urged calm about the rodent-borne disease, saying it is common across northern China and easily preventable through vaccination.