A UN human rights committee has heard there were credible reports that China is holding a million ethnic Uighurs in "counter-extremism centres".
She said she was concerned by reports that Beijing had "turned the Uighur autonomous region into something that resembles a massive internment camp".
China has not responded to the reports. Beijing has previously denied the existence of such camps.
Its 50-strong delegation said it would address questions on Monday, when the session in Geneva continues.
The Uighurs are a Muslim ethnic minority mostly based in China's Xinjiang province. They make up around 45 per cent of the population there.
Human rights groups including Amnesty International and Human Rights Watch have submitted reports to the UN committee documenting claims of mass imprisonment, in camps where inmates are forced to swear loyalty to Chinese President Xi Jinping.
The World Uyghur Congress said in a report that detainees are held indefinitely without charge, and forced to shout Communist Party slogans.
It said they are poorly fed, and reports of torture are widespread.
Most inmates have never been charged with a crime, it is claimed, and do not receive legal representation.
The reports come on a day of worsening religious tensions elsewhere in China, the BBC reported.
In Ningxia region, hundreds of Muslims engaged in a standoff with authorities on Friday to prevent their mosque from being demolished.
Officials said the newly-built Weizhou Grand Mosque had not been given proper building permits.
--IANS
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