Almost all flights in and out of Urumqi, capital of China's far-western Xinjiang region, have been cancelled because of a coronavirus outbreak.
The city has just six confirmed cases with symptoms and 11 asymptomatic infections, official figures show.
Strict measures to rein in the virus include stopping the single metro line and many public buses from operating.
After the pandemic emerged in China in late 2019, the country has driven new infections to consistently low levels.
To avoid a second wave, even small clusters are taken very seriously by health authorities. The initial outbreak in the city of Wuhan was brought under control through some of the world's strictest lockdown measures.
In Xinjiang, the government is promising decisive measures to contain the outbreak, according to local media reports.
More than 600 flights into and out of Urumqi Diwopu International Airport, more than 80% of Friday's total, were cancelled. Some social media users in the city say they have been told not to leave their housing estates.
Other social accounts suggested people were being stopped from entering or leaving Kashgar, another city in Xinjiang.