The northern city of Xi'an dramatically tightened Covid travel controls on Wednesday to fight a growing outbreak, with people banned from boarding trains without official permission and hundreds of flights cancelled.
With Beijing preparing to host the 2022 Winter Olympics in February, China is on high alert as it fights local outbreaks in several cities.
Xi'an reported 52 new coronavirus cases on Wednesday, bringing the total to 143 since December 9.
From Wednesday, residents are blocked from leaving the city by train without an official letter stating the trip is essential, state broadcaster CCTV reported.
It came a day after the city began testing all of its 13 million residents.
Around 90 residential areas were locked down, a government notice said on Tuesday, though it did not specify how many people were affected by them.
Long-distance bus stations were closed and authorities have set up disease control checkpoints on highways out of Xi'an, government notices said.
Inside the city, passenger capacity has been slashed on buses and trains, and schools closed.
Large indoor recreation venues remain shuttered, while the museum housing the world-famous Terracotta Army, has shut until further notice.
The city of Dongxing in Guangxi on Tuesday ordered its 200,000 residents to isolate at home after an infection was detected. (AFP)