China has denied it holds political prisoners and said its government prohibited the use of torture as it faced a United Nations review of its record, drawing the derision of exiled dissidents.

Winding up two days of scrutiny of China's human rights performance by the UN's Committee Against Torture, senior Chinese officials evaded questions about the number of police or prison guards prosecuted for torture, and the treatment of high-profile prisoners including several who had died in custody.

"The Chinese government prohibits torture and prosecutes any personnel or state organs for torture activities," said Li Wensheng, deputy director-general of the Ministry of Public Security's legal affairs department, while addressing the committee.

"There are plenty of cases involving prosecution of torture offenders," he added, without giving figures requested repeatedly by the 10 independent experts who monitor compliance with a UN anti-torture treaty ratified by China.

The UN experts pressed Chinese officials a day earlier about persistent allegations that torture is rife in China's police stations and prisons, especially of political prisoners, and about deaths in custody.

"There are no such cases of political prisoners," said Jin Chunzi of the State Ethnic Affairs Commission. "The allegation of cruel treatment of suspects from ethnic minority groups is groundless."

Committee chairman Claudio Grossman said in his summary: "I was surprised to hear that solitary confinement is a 'management tool'. I want clarification because it is certainly perceived as a penalty."

The experts questioned the use of electric shocks and rigid interrogation chairs which left inmates in painful positions for long periods.

"We use the interrogation chair to guarantee the safety of the detainee, to prevent the detainee from escaping, from self-harm or attacking other people," said Mr Li.

"The chair is sometimes packaged with soft padding to increase a sense of comfort, a sense of safety."

Golog Jigme, a prominent Tibetan monk who broke out of a Chinese detention centre in 2012 and attended the session after receiving Swiss asylum last month, voiced disappointment.

"Back in Tibet I was used to Chinese propaganda and to hearing lies each and every time there were communications by the Chinese government," he told Reuters. "I can honestly say there was not the slightest truth in anything they said today.

High-profile Tibetan monk Tenzin Delek Rinpoche died in a Chinese jail in July 2015. ( Supplied: Students for a Free Tibet )

"Regarding the interrogation chair, which was highly debated today, they said it was for the detainee's safety. Look at my wounds, on my hands and feet, in fact it was brutal torture."

Dolkun Isa of the World Uyghur Congress told Reuters: "Most answers are not the reality, they are avoiding to answer the questions ... I am not optimistic China will really do some improvements."

The UN expert committee, who also asked Hong Kong officials about excessive use of force in quelling the so-called umbrella protest movement last year, are due to issue their findings on December 9.

"China's efforts in combating torture will never cease," said Wu Hailong, China's ambassador who headed its delegation. "We are looking forward to an objective, impartial and professional evaluation."

Reuters