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

Most of the contaminations occurred in Xi'an, in the province of Shaanxi (northwest), where 13 million inhabitants have been confined since Thursday.

China is on high alert as it prepares to host the Winter Olympics in February in the capital Beijing.

As the country has reduced the number of cases to a minimum thanks to a "zero Covid" strategy that includes border restrictions, long quarantines and targeted lockdowns, cases have multiplied in recent weeks.

CCTV public broadcaster footage on Saturday showed long lines outside testing centers in Xi'an, as authorities rushed to stem the latest outbreak.

A security guard checks the documents of a resident during a lockdown in Xi'an on December 23, 2021 in China STR AFP

Under strict containment rules, as of Thursday, households in Xi'an are no longer allowed to send one member outside every two days to buy basic necessities.

Residents must obtain special permission from their employer or local authorities to leave the city.

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

But some 26 Xi'an government officials have been sanctioned for failing to prevent the virus, the Chinese disciplinary body said on Friday.

Local authorities who are believed to have failed to control the virus in their area are regularly fired or reprimanded as part of Beijing's strict approach.

Spraying disinfectant on a street in Xi'an, December 22, 2021 in China STR AFP / Archives

Xi'an's cases have so far spread to five other cities, including Beijing, according to state media, fueling fears about how quickly the virus is spreading in the country.

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

© 2021 AFP