China has hit back at UN criticism of its human rights record, saying a group of detained lawyers had committed serious economic crimes and missing Hong Kong bookseller Lee Bo was assisting a police enquiry and did not want publicity.

"Lee repeatedly clarified that he voluntarily went back to mainland for assisting in the investigation, and is safe and sound," China's mission in Geneva said in a statement on Tuesday. "Lee hopes that the general public respect his personal choice and privacy and do not hype up attention on the case."

Another bookseller, Gui Minhai, left the country in 2004 after being handed a suspended sentence for killing a student by drunk driving, but gave himself up to police in October, and was also involved in other crimes, the statement said.

Earlier on Tuesday, the UN High Commissioner for Human Rights, Zeid Ra'ad Al Hussein, had voiced concern for the booksellers, and also urged China to release all lawyers detained in a crackdown that began last July.

"The Chinese Mission expresses strong dissatisfaction and disagreement with the High Commissioner's misleading remarks," it said.

The case of the "so-called 'lawyers'" had been a crackdown on a major criminal gang for seriously disturbing social order, it said.

The gang had used the Beijing Fengrui Law Firm to organize crimes such as breaking into public security, procuratorial and judicial organs and courts, and gathering crowds and making disturbances in public venues, severely disrupting social order and judicial process, it said.