In July, a former teacher at one of the camps who fled to Kazakhstan told a court there that "in China they call it a political camp but really it was a prison in the mountains".
The New York Times quoted former detainees as saying that they were forced to sing songs such as "Without the Communist Party, There Would Be No New China" and those who could not remember the words were not given breakfast.
"In the end, all the officials had one key point. The greatness of the Chinese Communist Party, the backwardness of Uighur culture and the advanced nature of Chinese culture," former detainee Abdusalam Muhemet told the newspaper.
The World Uyghur Congress said in a report that detainees were held indefinitely without charge, and forced to shout Communist Party slogans.
It said they were poorly fed, and reports of torture were widespread.
Most inmates have never been charged with a crime, it is claimed, and do not receive legal representation.