China Saturday reported its highest number of new coronavirus cases in four months as officials rushed to contain outbreaks in several regions, including Xi'an city where millions are still under lockdown.

China, where the coronavirus was first detected in late 2019, is on high alert for new infections as it prepares to hold the Winter Olympics in February in the capital Beijing.

Of the 140 new infections, 87 were locally transmitted, according to a statement by the National Health Commission, compared to 55 a day earlier.

Most were in Xi'an, in the northwestern province of Shaanxi, where 13 million residents have been under lockdown since Thursday.

On Christmas Eve the city reported its highest daily count in a year with 75 domestic cases, according to the local health bureau Saturday.

While China has reduced cases to a minimum -- thanks to a zero-Covid strategy of tight border restrictions, lengthy quarantines and targeted lockdowns -- cases have been bubbling up in recent weeks.

Footage from state broadcaster CCTV Saturday showed long queues outside Xi'an testing centres as officials rushed to stamp out the latest flareup.

Under strict lockdown rules, since Thursday all households in Xi'an have only been permitted to send one member outside every two days to purchase necessities. Residents need special permission from their employer or local authorities to leave the city.

Xi'an has recorded 330 locally transmitted symptomatic cases since the first case was reported on December 9 2021, few compared to outbreaks elsewhere in the world.

But some 26 Xi'an government officials have been punished for lapses in virus prevention, China's disciplinary body said Friday.

Local authorities who are deemed to have failed at controlling the virus in their region are regularly sacked or reprimanded under Beijing's strict zero-Covid approach.

Cases from Xi'an have so far spread to five other cities including Beijing, according to state media, fuelling fears about how quickly the virus can spread geographically across the vast country.

China has reported 100,871 symptomatic cases and fewer than 5,000 deaths since the virus first emerged in the city of Wuhan in late 2019.