In a major ethical leap for the tech world, Chinese start-ups have built algorithms that the government uses to track [Uighurs] members of a largely Muslim minority group

Article is from April, found it linked from this BBC article from today: China due to introduce face scans for mobile users

A few highlights:

One Chinese start-up, CloudWalk, outlined a sample experience in marketing its own surveillance systems. The technology, it said, could recognize “sensitive groups of people.”
“If originally one Uighur lives in a neighborhood, and within 20 days six Uighurs appear,” it said on its website, “it immediately sends alarms” to law enforcement.

[facial recognition products] help advance China’s architecture for social control. To make the algorithms work, the police have put together face-image databases for people with criminal records, mental illnesses, records of drug use, and those who petitioned the government over grievances, according to two of the people and procurement documents.

The software extends the state’s ability to label Uighurs to the rest of the country. One national database stores the faces of all Uighurs who leave Xinjiang, according to two of the people.

...a procurement document for Hebei Province described how the police should be notified when multiple Uighurs booked the same flight on the same day.

Of course, all this takes place in the context of China's concentration camps for Uighurs:

China’s Repression of Uighurs in Xinjiang: More than a million Muslims have been arbitrarily detained in China’s Xinjiang Province. The reeducation camps are just one part of the government’s crackdown on Uighurs.