China is facing mounting criticism from around the world over its treatment of the mostly Muslim Uighur population in the north-western region of Xinjiang.
Human rights groups believe China has detained more than a million Uighurs over the past few years in what the state defines as "re-education camps".
There is evidence of Uighurs being used as forced labour and of women being forcibly sterilised.
The US is among several countries to have accused China of committing genocide and crimes against humanity through its repression of the Uighurs.
China denies such allegations, saying it has been combatting separatism and Islamist militancy in the region.
Who are the Uighurs?
There are about 12 million Uighurs, mostly Muslim, living in north-western China in the region of Xinjiang, officially known as the Xinjiang Uyghur Autonomous Region (XUAR).
The Uighurs speak their own language, similar to Turkish, and see themselves as culturally and ethnically close to Central Asian nations.
They make up less than half of the Xinjiang population.
Recent decades saw a mass migration of Han Chinese (China's ethnic majority) to Xinjiang, and the Uighurs feel their culture and livelihoods are under threat.
Where is Xinjiang?
Xinjiang lies in the north-west of China and is the country's biggest region.
Like Tibet, it is autonomous, meaning - in theory - it has some powers of self-governance. But in practice, both face major restrictions by the central government.
It is a mostly desert region, producing about a fifth of the world's cotton.
It is also rich in oil and natural gas and because of its proximity to Central Asia and Europe is seen by Beijing as an important trade link.
In the early 20th Century, the Uighurs briefly declared independence, but the region was brought under the complete control of China's new Communist government in 1949.
What are the allegations against China?
Several countries, including the US, Canada and the Netherlands, have accused China of committing genocide - defined by international convention as the "intent to destroy, in whole or in part, a national, ethnical, racial or religious group".
It follows reports that, as well as interning Uighurs in camps, China has been forcibly mass sterilising Uighur women to suppress the population and separating Uighur children from their families.
US Secretary of State Antony Blinken has said China is committing "genocide and crimes against humanity".
UK Foreign Secretary Dominic Raab has said the treatment of Uighurs amounts to "appalling violations of the most basic human rights".
A UN human rights committee in 2018 said it had credible reports the Chinese were holding up to a million people in "counter-extremism centres" in Xinjiang.
The Australian Strategic Policy Institute found evidence in 2020 of more than 380 of these "re-education camps" in Xinjiang, an increase of 40% on previous estimates.
Earlier, leaked documents known as the China Cables made clear that the camps were intended to be run as high security prisons, with strict discipline and punishments.
People who have managed to escape the camps have reported physical, mental and sexual torture - women have spoken of mass rape and sexual abuse.
In December 2020 research seen by the BBC showed up to half a million people were being forced to pick cotton. There is evidence new factories have been built within the grounds of the re-education camps.
What was the build-up to the crackdown?
Anti-Han and separatist sentiment rose in Xinjiang from the 1990s, flaring into violence on occasion. In 2009 some 200 people died in clashes in Xinjiang, which the Chinese blamed on Uighurs who want their own state. But in recent years a massive security crackdown has crushed dissent.
Xinjiang is now covered by a pervasive network of surveillance, including police, checkpoints, and cameras that scan everything from number plates to individual faces. According to Human Rights Watch, police are also using a mobile app to monitor peoples' behaviour, such as how much electricity they are using and how often they use their front door.
Since 2017 when President Xi Jinping issued an order saying all religions in China should be Chinese in orientation, there have been further crackdowns. Campaigners say China is trying to eradicate Uighur culture.
What does China say?
China has said reports it has detained Uighurs are completely untrue.
It says the crackdown is necessary to prevent terrorism and root out Islamist extremism and the camps are an effective tool for re-educating inmates in its fight against terrorism.
It insists that Uighur militants are waging a violent campaign for an independent state by plotting bombings, sabotage and civic unrest, but it is accused of exaggerating the threat in order to justify repression of the Uighurs.
China has dismissed claims it is trying to reduce the Uighur population through mass sterilisations as "baseless", and says allegations of forced labour are "completely fabricated".