BEIJING — China has turned its western region of Xinjiang into a police state with few modern parallels, employing a combination of high-tech surveillance and enormous manpower to monitor and subdue the area’s predominantly Muslim ethnic minorities.

Now, the digital dragnet is expanding beyond Xinjiang’s residents, ensnaring tourists, traders and other visitors — and digging deep into their smartphones.

A team of journalists from The New York Times and other publications examined a policing app used in the region, getting a rare look inside the intrusive technologies that China is deploying in the name of quelling Islamic radicalism and strengthening Communist Party rule in its Far West. The use of the app has not been previously reported.

China’s border authorities routinely install the app on smartphones belonging to travelers who enter Xinjiang by land from Central Asia, according to several people interviewed by the journalists who crossed the border recently and requested anonymity to avoid government retaliation . Chinese officials also installed the app on the phone of one of the journalists during a recent border crossing. Visitors were required to turn over their devices to be allowed into Xinjiang.