But the Chinese government has fired back through its representatives in New Zealand.

"We're firmly opposed to any attempts to sabotage China's sovereignty and territorial integrity," an embassy spokesperson told Newshub.

"Certain people seemed to be blindfolded by some fake news and clouded by falsehoods. We hope they could view China's counter-terrorism and deradicalization efforts in an objective way."

UN experts and activists say at least one million Uighurs and members of other largely Muslim minority groups have been detained in camps in Xinjiang since 2017.

Human rights groups and former detainees have said conditions in the camps are poor, with inmates subject to psychological and physical abuse.

Claims about the detention camps themselves are hard to verify as China only allows periodic supervised visits and gives little information on their operations.

Beijing says it is providing vocational training to help stamp out separatism and to teach new skills. It describes the detainees as students and denies any mistreatment of Uighurs.

"Xinjiang-related issues are China's internal Affairs, they're not about human rights or religion, but about fighting violence, terrorism and separatism," the Chinese spokesperson told Newshub.

"The Chinese government protects our citizens' freedom of religious belief, including the Uighur ethnic group, in accordance with law.

"The measures taken by the Chinese government to fight terrorism and maintain stability in Xinjiang are endorsed by local people of various ethnic groups. Xinjiang has not experienced a single terrorist attack for three years in a row."

Williams has been offered the chance to visit Xinjiang himself and see what conditions are like for himself.

"We welcome all those who have unbiased minds to visit China including Xinjiang and see the place with their own eyes," the embassy says.