Xi an is about 900 km (560 miles) from China s Olympics venues. AFP
China has stuck to a "zero-Covid" strategy involving tight border restrictions, lengthy quarantines and targeted lockdowns.
Authorities have been especially vigilant in recent months to avoid an outbreak before February's Beijing Winter Olympics, but there have been sporadic flare-ups.
But on Sunday the country reported 206 new Covid infections -- the highest daily number since March 2020.
"In the coming days, a number of cases are still likely to be detected," Xi'an official He Wenquan warned, calling on the city's population not to panic.
The northern metropolis -- about 900 km (560 miles) from the Olympics venues -- reported 155 new Covid patients on Sunday, bringing the total to nearly 500 over the past few weeks.
About 29,000 people have been placed in hotel quarantine, He said.
Xi'an residents have already been tested several times, authorities said, and a "total" disinfection was to begin Sunday evening.
Restrictions on movement have also been tightened.
Each household can only send one member out to buy basic necessities once every three days -- down from two days under previous rules.
All businesses except supermarkets, convenience stores and medical facilities have been ordered to close.
Since the coronavirus first emerged in the central city of Wuhan in late 2019, China has largely kept the pandemic at bay.
The country has officially recorded only two deaths in over a year.