The documents were leaked to The New York Times by a member of the Chinese political establishment in an effort to hold President Xi accountable for the mass detentions.
An Uighur human rights group says that China has more than 500 detention centres, prisons and "re-education camps" in Xinjiang.
China has detained over one million Uighur Muslims in Xinjiang over the past three years.
Human rights groups say these so-called re-education camps are an attempt to suppress the Uighurs' religion and Islamic identity by involuntarily detaining them without trial, sometimes with threats of violence and torture.
According to the documents, in response to a spate of violent attacks carried out by Uighur militants in 2014, Xi told party leaders that they needed to "be as harsh as them and show absolutely no mercy."
Xi hinted at the internment camps in one speech, although he did not call for mass detention outrightly and resisted banning Islam in the country entirely.
"There must be effective educational remolding and transformation of criminals. And even after these people are released, their education and transformation must continue," he had said.
The Chinese government has denied any human rights abuses, saying that the efforts are important in combating extremism and terrorism.
The leaked papers consist of 24 documents, including nearly 200 pages of internal speeches by Xi and other leaders, and more than 150 pages of directives and reports on the surveillance and control of the Uighur population in Xinjiang.
There are also references to plans to extend restrictions on Islam to other parts of China.
The Communist Party also has a special manual instructing officials on how to deal with Uighur students who get back from university to find that their families have been imprisoned as part of the mass detention.
When students ask where their relatives are, officials are told to say: "They're in a training school set up by the government to undergo collective systematic training, study and instruction."
The manual encourages officials to liken the detained relatives' mental state to having a serious, contagious disease like SARS, which requires the "quarantine" of Uighur detention camps.
"If you were careless and caught an infectious virus like SARS, you'd have to undergo enclosed, isolated treatment, because it's an infectious illness," it says.
The Uighurs are a mostly-Muslim ethnic minority largely based in Xinjiang in western China. Many Uighurs call the region East Turkestan.
A number of Uighurs have been arrested or forced into detention on flimsy charges, such as texting people outside Xinjiang or setting their clocks to two hours ahead of Beijing's time zone to align with Xinjiang's natural daylight schedule.
The documents also tell officials to say that detainees "have very good conditions for studying and living there," and that tuition, food and living costs are all free of charge.
Former detainees have described the detention centres as being overcrowded and having almost nonexistent hygiene standards. They have also recalled being shackled to chairs and forced to sing propaganda songs to get food.
Another part of the document says that "training" has to be behind closed doors "otherwise, they will never be able to thoroughly eradicate this stubborn cancer in their thinking and could easily again be swindled and exploited."
"Treasure this chance for free education that the party and government has provided to thoroughly eradicate erroneous thinking, and also to learn Chinese and job skills. This offers a great foundation for a happy life for your family," officials are told to say.
Many relatives of detained Uighurs in Xinjiang say their relatives are professionals such as doctors and editors and do not need vocational training.
( With inputs from IANS )