Beijing, China: The northern Chinese city of Xi'an on Wednesday has ordered lockdown and has asked its 13 million residents to stay at home supporting in fighting the 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.

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 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.