Amid preparations for mega-events, including New Year holidays and the Beijing Winter Olympics, rising coronavirus cases have brought enhanced restrictions in parts of China.
The latest hotspot of COVID-19 in the country saw a jump in locally transmitted cases over the past few days.
China's National Health Commission (NHC) said in a statement that the country reported 182 locally transmitted cases on Monday.
Of the 182 cases, the NHC said, 180 were found in northwestern Shaanxi province, with the local capital Xi'an reporting a single-day high of 175 cases.
The city is now under lockdown after it detected transmissions of the infection last week and has so far reported over 100 cases for three consecutive days.
On Sunday, the Chinese mainland reported 162 new locally transmitted COVID-19 cases -- the highest number in over 20 months.
The NHC said 27 new imported cases were reported in 10 provincial-level regions, while no new coronavirus-related deaths have been registered.
Xi'an is around 901 kilometers (560 miles) from the Olympics venue, but authorities are imposing strict cross-border measures to avoid the spread of the infection in other places.
A city of 13 million, Xi'an began a new round of mass nucleic acid testing on Monday to curb infection with more than 5,000 sample-collecting venues and 31,000 staff.
It detected its first case on Dec. 9 -- a staffer engaged in disinfection at a quarantined hotel for inbound flights, with the ongoing transmission of infection linked to the delta variant.
A total of 635 COVID-19 cases have been confirmed in the capital so far.
The omicron variant in China is linked to an imported case of an inbound flight on Dec. 4.
"Many positive cases didn't show obvious symptoms in the initial stage. Therefore, they tended to ignore their physical condition, which led to the rapid spread of the virus inadvertently," said Wei Xiaoli, deputy director of the city's disease control and prevention center.
After the local authorities imposed strict lockdown measures in communities and villages last Thursday, "long-distance passenger transport lines have been suspended, except for freight vehicles transporting epidemic prevention materials and daily necessities," said a report by the state-run Xinhua News.
"Taxis and drivers working for online ride-hailing platforms may not enter medium or high-risk areas or travel outside the city," it added.
“For Xi’an, intensified control and screening measures are urgent to block the virus as soon as possible,” said Zhang Boli, an academic at the Chinese Academy of Engineering, told Xinhua.
“I estimate the transmission will be cut off in mid-January and the outbreak can be completely put under control in late January. It is very possible,” he added.
Last weekend, under intense anti-pandemic measures, 135,000 students in Xi'an sat in exams as educational institutions have been shut, affecting close to 2 million people.
China has reported 101,486 COVID-19 cases as of Monday, including 4,636 deaths.
