When Abel Amantay, an ethnically Kazakh citizen of China, returned to the western Chinese region of Xinjiang last year to register his Kazakhstan green card, he was detained and sent to Jinghe county’s “re-education centre” in Bortala prefecture.

After finally obtaining permission this month to visit the Xinjiang facility, Mr Amantay’s father saw his son and learnt that he was employed in the centre’s textile factory earning Rmb650 ($95) a month. Mr Amantay is now allowed to make brief, twice-monthly supervised calls to his wife in Kazakhstan.

“He does not say much and just said he is learning a lot. But every time he calls, he asks for the children’s names, ages, which grade they are in,” said Aiytkali Ganiguli, Mr Amantay’s wife and a Kazakh citizen. “He sounds like he has severe memory loss.”

Before its abolition in 2013, China’s gulag-style laojiao system of re-education through work forced millions deemed to be political dissidents to perform hard labour. The emergence of a forced labour system within Xinjiang’s internment camps this year suggests Beijing is resurrecting elements of laojiao, with Mr Amantay becoming one of its latest victims.

“The similarities between what is happening to Uighurs and what happened to people with unwanted political backgrounds in the Maoist period are striking . . . except [this time] only members of particular minority ethnic groups are targeted for this extralegal form of forced labour,” said Darren Byler, an anthropologist at the University of Washington who specialises in Xinjiang.

In early 2017, Chinese authorities began using extralegal detention against Uighur Muslims and other minorities, including Kazakhs, in internment camps. The UN estimates least 1m people are being held in such facilities and China has been condemned internationally.

Beijing has recast the internment camps as “vocational education centres” intended to eradicate supposed extremist tendencies in detainees by teaching them Communist doctrine and the Mandarin language.

Chinese authorities have taken that further by constructing forced labour facilities within internment camps as Xinjiang expands the scope of its mass detention system.

In interviews with the families of six Uighur and Kazakh detainees, relatives said detainees have been employed at textile factories with little to no pay after “graduating” from the region’s detention centres. They are not allowed to leave the factories and communication with relatives, if permitted, is heavily monitored.

“He kept saying, there are things I cannot say more about because there is a police person behind me,” said Sara Zhienbai, a Kazakh citizen who lost contact with her husband Dakey Juniskhan after he was detained on New Year’s Day in Xinjiang’s Ili prefecture. He was allowed a two-minute phone call in October to tell relatives he had been transferred from an internment centre to a factory.

Two of Xinjiang’s largest internment camps — the Kashgar city and Yutian county vocational training centres — have opened forced labour facilities this year. Yutian’s detention centre boasts eight factories specialising in vocations such as shoemaking, mobile phone assembly and tea packaging, offering a base monthly salary of Rmb1,500 ($220), according to Chinese state media reports.

Satellite images show that Kashgar’s internment centre has more than doubled in size since 2016 and Yutian’s grew 269 per cent over the same period, according to a report compiled by the Australian Strategic Policy Institute, a think-tank.

State media say that such labour is voluntary and jobs are selected by students after they “pass language standards and learn the law”.

“A life distorted by religious extremism needs to be saved. A soul poisoned by religious extremism needs to be awakened,” according to a November report in the party-run Xinjiang Daily. “After vocational skills education and training, the students clearly identified right from wrong, changed their minds and broke with their dark past, ushering in a new life.”

Xinjiang authorities did not respond to a request for comment.

“This is not voluntary work,” said Omirbek Nurmukamet, whose Chinese-born wife Zhainbar Daulet was detained last July in Xinjiang’s Hutubi county in Changji prefecture.

Ms Daulet has been performing forced labour in Hutubi since September, according to her husband. “She works in a textile factory and, in her spare time, she learns Mandarin and party propaganda. The hours are long,” he said.

People assigned to the factories appear to be subject to a less stringent regime than those in the main internment camps, as they are allowed to receive monitored monthly visits and short calls from family members.

“His ‘teacher’ in the camp said that he had studied political teaching very well and his Chinese was very good, which was why he was able to ‘graduate’ to garment factory work,” according to one detainee’s brother, who declined to provide his name as he and his family live in China. The detainee, a Uighur dentist, was taught to operate a sewing machine and “sentenced” to three years labour in November, according to his family.

But others say they have been cut off from their detained loved ones, while calls to officials and relatives within China go unanswered.

Razila Nurala, a 25-year-old Chinese vocational graduate who moved with her family to Kazakhstan in 2016, was detained in August in Xinjiang’s Chitai county internment centre after returning to work at a marketing agency. In November, she was put to work in a textile factory.

“It is unnecessary to send my daughter to re-education because she is very highly educated and has valuable work experience,” said Kaliasgar Nurbak, her mother, now a naturalised Kazakh citizen.

In November, Ms Nurala’s aunt was able to visit her in Chitai county. Ms Nurala told her she was not being paid a wage and had hurt her hand operating the factory machines but appeared too nervous to say more.

“No one can contact her, and she is not allowed to go home,” said Ms Nurbak. “She is all alone.”

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