- Video report by ITV News Asia Correspondent Debi Edward
In China, an estimated one and a half million people are held behind wire fences. Their crime is their refusal to denounce their religion.
Beijing has routinely been accused of detaining Muslims in what detainees call "concentration camps".
It is thought there are 70 of the camps in the country, and that number is growing.
Only recently did an admission of the existence of such "reeducation centres" come from the country's government. It insists they serve a purpose of preventing extremism and denies any wrongdoing.
But the families of detainees say those taken there are kept in demeaning conditions.
Some who do escape flee to Kazakstan - there they stay in refugee camps, waiting for their family members to return.
One 14-year-old boy spoken to by ITV News hasn't seen his mother and two sisters since they were detained.
"I haven't seen my mother for two years. She's 45-years-old and my father is dead," he said.
"I am all alone in this world."
Others have stories even more harrowing.
Axel is just 16-years-old, yet he has thought about taking his life after his family members were detained.
He said: "I'm now 16, I'm becoming a man, and what I need by dad most, he's not here."
Another woman ITV News spoke to says Chinese authorities detained her.
She was seen on camera crying but refused to apologise. Her punishment was to be handcuffed and made to sit in a stress position for six hours.
Back in China, the persecution of Muslims has extended to the demolition of mosques and the arrest of worshippers accused of illegal religious education.
At Beijing's oldest and largest place of worship for Muslims, the Niu Je Mosque, a Chinese flag stands where a minaret once did; an undeniabe symbol of the state's authority over the people.
Where prayer once happened, people are now concerned their detention is imminent.
Defending its actions, a Chinese government spokesperson said: "The purpose of establishing educational training centres in Xinjiang is clear.
"It is to prevent terrorism and extremism - as for whether China has an anti-Islam policy, I can definitively say there is no such policy."