So far, at least five cases linked to Urumqi have been discovered, including a man who was confirmed positive after he travelled from the city to the eastern province of Zhejiang, state media said.

The infections were detected beginning on Wednesday, and news of the cases prompted state media outlets in Urumqi to issue assurances on Friday that supermarkets had ample stocks of food -- an apparent attempt to discourage panic-buying.

The new cases illustrate the continuing difficulty China faces in stamping out the contagion, which emerged in the central Chinese city of Wuhan late last year before spreading throughout the country and globally.

Strict lockdowns across the country and widespread COVID-19 testing largely brought the outbreak under control within Chinese borders.

But a new cluster emerged in Beijing in June, infecting more than 330 people before also being contained.

Aviation authorities announced that 89 percent of flights servicing Urumqi had been cancelled, and the metro system said the city's single line had been shut down from late Thursday.

Neither of the brief announcements indicated when normal service might be resumed.

Public bus services also were curtailed and the vehicles subjected to thorough disinfection while bus employees would be required to take COVID-19 tests, bus authorities announced.

China has reported a total of more than 83,000 infections and 4,634 deaths.

Around half of Xinjiang's population of more than 21 million is composed of ethnic Uighurs and other Turkic Muslims, many of whom complain of decades of political and religious oppression by China's ruling Communist Party, which the government denies.