The call came as People’s Daily said Beijing Fengrui law firm director  Zhou Shifeng had confessed in custody that his firm had been involved in “criminal activities”.

China Central Television described Zhou and his lawyers as a “criminal gang” that had “manipulated, organised and hyped up cases”.

Legal experts say confessions from those in mainland custody are often extracted through physical and mental torture.

Amnesty International China researcher William Nee  said that reporting on the detainees’ confessions before they had been charged and the portrayal of them as criminals “calls into question whether they can get fair trials”.

Apart from six people already in criminal detention, People’s Daily said more lawyers had been subject to unspecified forms of detention. They were Xie Yuandong,  a trainee lawyer at Fengrui, and other non-Fengrui lawyers: Li Heping,  Xie Yanyi,  Xie Yang,  Liu Jianjun, and Sui Muqing.  It also said activists Wu Gan, nicknamed “Super Vulgar Butcher”, and Zhai Yanmin  were also under “coercive measures”.

Xinhua said last month that Zhai and Liu were detained on the charge of “disturbing social order” for organising protests.

Rights groups said earlier that Sui and Xie Yang were subject to “residential surveillance” – a form of detention that can last up to six months – on the charge of “incitement of subversion of state power”.

People’s Daily said last weekend that Zhou, his assistant Liu Sixin,  lawyers  Wang Quanzhang, Huang Liqun,  Wang Yu and her husband Bao Longjun  were in criminal detention for “seriously violating the law” but did not specify a charge.

It described the Fengrui law firm as “a platform” used by a “criminal gang” that constituted lawyers, activists and petitioners who “colluded and provoked trouble”.

Quoting alleged testimony from detained Fengrui staff and activists, the report on Sunday accused Zhou of unprofessional conduct, including embezzlement and bribery and “inappropriate sexual relations”.

They said Zhou often encouraged his lawyers to work with activists and petitioners to “incite” protests and to “blow up issues on the internet” to draw publicity to influence court outcomes.

“I condoned and encouraged these unlawful activities … and these have an impact on social stability. I have unshirkable responsibilities,” Zhou allegedly said.

People’s Daily accused Zhou and his lawyers of becoming involved in rights cases for fame and monetary gain.

“Now, Zhou Shifeng is deeply regretful,” the article said.

Nee said he was concerned that the detainees could have been forced to confess.

“All the lawyers who have been detained are at risk of torture or other ill treatment since the government seems to be emphasising the role of confessions in proving its pre-set narrative,” he said.

The China Human Rights Lawyers Concern Group said Wang Yu’s 16-year-old son was interrogated by police four times, and his house keys and passport had been confiscated so he could not go to study in Australia as planned. The family was also barred from hiring a lawyer.

Political analyst Johnny Lau Yui-siu said the smear campaign and the targeting of detainee’s family was a revival of Cultural Revolution-era practice and made a mockery of the party’s promise to rule by law. 

Additional reporting by Danny Lee