ABC News Senior Investigative Producer Gerry Wagschal was granted rare on-camera tours of two centers in Xinjiang: One in Shule County outside the ancient Silk Road city of Kashgar, which the center's director said houses about 1,000 Muslim detainees, and another outside the city of Artux.
The Chinese officials on the tour called the detainees "students," and said they were enrolled because they had been influenced by extremist ideologies.
"We cannot go outside," Mihrigul Tursun told ABC News as she recalled her time being detained in one of the Chinese centers.
Tursun, who is the first outspoken camp survivor to seek asylum in the United States, said she was starved, isolated and unable to shower for weeks on end. She said Chinese authorities believed she was a terrorist because she had traveled to Egypt several times in the past, and that they had told her Egypt was considered a "dangerous country."
"I am not a terrorist," Tursun said she had told Chinese authorities numerous times while being detained.
The Chinese government disputes that Tursun was detained for as long as she claims, but concedes that she was detained.
Touring the 'vocational' centers
During its tour of the centers, ABC News witnessed the so-called "students" attend classes where they learned China's laws, regulations and the Mandarin language. Many of these "students" told ABC News that they were grateful to be in the camps.
"If not for the [Chinese] government, I would someday become a terrorist," said one detainee while wiping tears from his eyes.
All of the detainees ABC News was granted permission to speak with said they had "applied" to go to these "vocational centers" — a name given by the Chinese government — and that they were being detained voluntarily.
However, despite what ABC News was shown on its tour, academic researchers knowledgeable in the region say these chaperoned tours are highly orchestrated and staged prior to media arrival.
"My research has shown that these camps are being modified prior to the visits," said Adrian Zenz, an independent researcher who studies China's minority policies. "Satellite images before and after show that several months before visits are permitted, watchtowers and other security features such as metal fencing were removed from these camps."
Upon the end of the government-guided tour, ABC News asked Chinese officials to see other centers in the region, specifically ones that satellite images showed had barbed wire fences and watchtowers. The requests were denied.
"Nobody goes to these facilities on a voluntary basis and there's no application process. ... Government documents never talk about any application," said Zenz.
The Chinese government is under international scrutiny for its use of these camps in Xinjiang, where the watchdog group Human Rights Watch says up to a million Muslims are held under inhumane conditions as part of China's "Strike Hard Campaign against Violent Terrorism."
"These are truly internment camps where these people are being treated in ways that are fundamentally inconsistent with what China would have you believe, and in ways that — when the world finds out — we will all regret," U.S. Secretary of State Mike Pompeo told ABC News.
Alleged detainees and family, friends speak out
Prior to being granted a tour of these centers, ABC News spoke with several ethnic Muslims who said they were detained inside these centers, including Tursun. These interviews were part of an eight-month-long investigation by ABC News' "Nightline."
Many of the ethnic Muslims who claim to have been detained in these centers say they were imprisoned simply because they were Muslim.
"When they took me, they did not say that they were taking me to prison," Kairat Samarkan told ABC News' Bob Woodruff, who traveled to Kazakhstan, a country bordering China's Xinjiang province, to speak to several people who claimed that they were held inside these centers.
Samarkansaid Chinese officials inside the center told him he was being detained for frequent travel between Kazakhstan and China. "The very fact that I was a Kazakh was a crime," Samarkantold Woodruff.
Along with alleged firsthand accounts from inside the camps, ABC News met dozens of people in both the United States and Kazakhstan who claim to have missing loved ones who they believe are being held prisoner inside these Chinese centers. One of these people was Kuzzat Altay.
"He sent me a message from WeChat," Altay told ABC News, recalling the last conversation he had with his father. "He said, 'Son, they are taking me.'"
Altay, 35, is a computer science teacher based in Virginia. He hasn't spoken to his father in over a year and believes he is detained inside one of China's centers, cut off from communication with the outside world.
"I see him in my dream[s] once in a while," Altay said. "That's the only place that I can see him."
In March, ABC News went to Kazakhstan to meet some of the families and friends of missing loved ones who are believed to be inside these centers. All of the people we spoke with were huddled in Serikzhan Bilash's office, which is located in the city of Almaty. Bilash is a Kazakh activist who works to defend Muslim minorities who say they've faced oppression in Xinjiang.
Bilash was arrested in March for inciting inter-ethnic hatred triggered by his call for an "information Jihad" against the Chinese authorities over their policies in Xinjiang. Shortly after Bilash's arrest, Kazakh police raided the activist's office and collected his files. The raid was captured on camera by "Nightline."
Bilash's wife, Leila, claimed the Chinese government was behind her husband's arrest. "I really think that China is standing behind his arrest because China really doesn't want to know about these concentration camps," she told "Nightline."
After he was released earlier this month, Bilash's lawyer told ABC News that his client had signed a plea deal agreeing to end his activism against China's Muslim policies in order to avoid a seven-year jail sentence.
ABC News reached out to the Chinese government in a two-page letter signed by the ABC News team about the many allegations of abuse against its Muslim population in Xinjiang. A spokesperson for China's Ministry of Foreign Affairs responded, saying shortly, "I can tell you clearly that none of the claims listed in the [letter from ABC News] corresponds with facts."
In July, the Chinese government said it would release those detained in its "vocational centers" after a certain period and that some have already been released. The U.S. State Department says there is no evidence to support that claim.
Following the statement from the Chinese government, Altay took to twitter, writing that if China did intend to release the Muslims interned in these centers, then "where is my father?"