This comes as people are preparing to move to their homes during the upcoming New Year holidays and as Beijing prepares to host Winter Olympics.
The National Health Commission (NHC) in its latest data showed the Chinese mainland on Sunday reporting 162 new locally transmitted COVID-19 cases, the state-run Xinhua News reported on Monday.
This was the highest number of cases over one and a half years.
Xi'an city, the capital of northwestern Shaanxi province -- the hotspot of the latest outbreak -- reported 152 of the total cases, the NHC said.
The city has been under lockdown imposed since last week in the wake of rising coronavirus cases.
Around 901 kilometers (560 miles) from the Olympics venue, Xi'an saw a jump in virus cases above a hundred on Sunday, bringing the total to 500 over the past few weeks.
Officials said close to 29,000 people are under hotel quarantine.
Health authorities in Xi'an are holding the third round of mass testing initiative since the first case was reported on Dec. 9.
During the holiday season, millions of people are expected to return home and visit tourist places which could complicate the situation further.
Public transport, including flights and trains, has been shut while more than 3,500 schools have been closed, affecting over 2 million students and staff.
According to the NHC, no new deaths from COVID-19 were reported on Sunday.
China has reported 101,277 confirmed COVID-19 cases, including 4,636 deaths, on the mainland as of Sunday.
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