Chinese authorities have ostensibly arrested thousands of terrorists in the country's largest region, Xinjiang, in the past five years as part of their effort to curtail the threat of Islamist militancy.

Hunter Biden, the second son of 2020 Democratic contender and former US vice president Joe Biden, is said to have bought into an app purportedly used in China's mass surveillance system in restive Xinjiang province.

Biden Jr., according to The Intercept, was found to be in "close proximity" to influential Chinese government and business figures.

Specifically, Hunter Biden's investment company in China, called Bohai Harvest RST (BHR), had reportedly ploughed millions of dollars into Face++, a facial recognition platform mentioned in a recent Human Rights Watch report.

Human Rights Watch said on Wednesday that it had obtained and examined an app that Chinese authorities allegedly use to spy on individuals living in the western province of Xinjiang, a flashpoint of terrorism where the mostly-Muslim ethnic minority of Uyghurs resides.

According to the advocacy group, the app flags suspicious individuals for officials, who later may subject them to certain restrictions, including banning them from leaving the country or placing them into so-called "re-education camps".

READ MORE: Diplomats From 8 States Arrived in China Over Reeducation Camps – Reports

The app is thought to use Face++ software to check whether the photo on a person's ID matches their face or for "cross-checking" pictures on two different documents.

However, Megvii, the owner of Face++, was reported to have denied any relationship with the Xinjiang mass surveillance system.

While Hunter Biden has yet to comment on his supposed connection with the Chinese mass surveillance system, it comes amid US criticism of Beijing's domestic policy.

However, Joe Biden has recently downplayed the threat that some US diplomats say Beijing poses to US security.

"China is going to eat our lunch? Come on, man!" Biden asked on Thursday. "The fact that they have this great division between the China Sea and the mountains in the East, I mean in the West. They can't figure out how they're going to deal with the corruption that exists within the system. They're not bad folks, folks. But guess what, they're not competition for us," he claimed.

Randall Schriver, a US Defence Department official, meanwhile, has accused Beijing of "mass imprisonment" of Chinese Muslims, pegging the number of detained Muslims at being "closer to 3 million citizens".

Since the 1990s, China's Xinjiang Uyghur Autonomous Region has seen a flurry of terror attacks which the authorities blame on religious extremism. The government stated in March it had arrested almost 13,000 terrorists in the region since 2014 and destroyed over 1,500 "violent and terrorist gangs".

READ MORE: Xinjiang Explores New Ways to Fight Terrorism — Expert on International Affairs

In response to last year's UN report on Muslim minorities in Xinjiang allegedly being placed in "internment camps", China's foreign ministry stated that the assumptions are based on "unsubstantiated and irresponsible information".

Shohrat Zakir, the chairman of the region, himself of Uyghur origin, called the UN estimates a "rumour" and stated that the camps in question were temporary vocational training and educational facilities.