Rights groups have warned that Bangkok is preparing to deport imminently a group of 48 members of China's mostly Muslim Uyghur minority, who are being held in immigration centres around Thailand.

The groups said they fled China -- which has been accused of grave human rights abuses in the Xinjiang region against Uyghurs -- more than a decade ago and live in constant fear of being sent back.

Thai authorities have repeatedly denied such a plan.

The United Nations human rights office has "been closely following these cases", spokeswoman Ravina Shamdasani told AFP on Friday.

"We have been in touch with the relevant authorities, encouraging a durable solution that would prevent anyone being returned to any country where they would face significant risks of harm, in line with Thailand's international human rights obligation and its own national law," she said in an email.

Her comment came after a group of independent UN rights experts earlier this week urged authorities to "immediately halt" the possible transfer, warning the Uyghurs faced "real risk of torture or other cruel, inhuman or degrading treatment or punishment" in China.

They said the 48 Uyghurs were detained after entering Thailand to seek protection, and that they have allegedly been held in de facto incommunicado detention for more than a decade, with no access to lawyers or family members.

Urging Thailand to help them access asylum procedures and humanitarian assistance, the experts said: "It is our view that these persons should not be returned to China... We are concerned they are at risk of suffering irreparable harm."

The experts, who are appointed by the UN Human Rights Council but who do not speak on behalf of the United Nations, said 23 of the 48 Uyghurs suffer from serious health conditions.

Human Rights Watch said last week that Thai immigration officials had asked the Uyghurs to complete new paperwork and had photographed them -- steps the rights group believes are in preparation for their forcible transfer.

HRW says the Uyghurs are on hunger strike, although Thai authorities have denied this.

The United States has branded China's treatment of the minority a "genocide".

A damning report released by the UN rights office in 2022 detailed violations including torture and forced labour and "large-scale" arbitrary detention in what China calls vocational training centres.

Beijing denies allegations of abuse and insists its actions in Xinjiang have helped to combat extremism.