Dozens of officials have been punished over a virus outbreak in the locked-down city of Xi'an, China's disciplinary body said Friday - the latest state reprimands under Beijing's strict zero-Covid approach.

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.

The world's most populous nation has reduced cases to a minimum thanks to a zero-Covid strategy of tight border restrictions, lengthy quarantines and targeted lockdowns.

But cases have been bubbling up in recent weeks -- with Xi'an, home to the world-famous Terracotta Warriors, telling all 13 million residents to stay home from Thursday, shuttering businesses and launching several rounds of mass testing.

The Central Commission for Discipline Inspection said Friday that 26 Communist Party officials had been punished for "insufficient rigour in preventing and controlling the outbreak".

Xi'an reported another 49 cases on Friday, bringing the total outbreak to more than 250 in recent weeks.

Chinese officials who are deemed to have failed at controlling the virus in their region are regularly sacked or reprimanded.

The statement said inspections had revealed there had been a lax approach to testing and an uncoordinated response that hindered contact tracing in Xi'an.

Authorities would clamp down on "bureaucratic issues in disease control work such as shirking responsibility, not taking action, passing the buck and dealing with things in a negative way", a Party discipline official said.

A party secretary in Inner Mongolia was sacked after his area was hit by a cluster of cases in October, while the head of Zhengzhou city's health commission was sacked in August after cases this summer.

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.

Under 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 who want to leave the city must first apply for approval, while major venues including the museum housing the Terracotta Army -- the mausoleum of China's first emperor -- have been shut until further notice.