Chinese security agents hooded one as they bundled him into a vehicle. Police seized others at home as their horrified families watched. More, alone when they disappeared, sent frantic text messages to friends.

Six months ago, China's biggest-ever crackdown on human rights lawyers saw state agents question more than 130 attorneys and their colleagues.

Among those who were taken away at least 16 people are still being held in secret, leaving their families isolated and fearful.

The sweep demonstrates the hollowness of the Communist Party's loudly proclaimed commitment to the rule of law, campaigners say, and is an attempt to end efforts to use China's tightly-controlled legal system to independently challenge official injustice.

Now dozens of the rights lawyers are trying to employ that same system to defend their absent colleagues.

"The Communist Party uses weapons to maintain its rule. We cannot use guns, but at least we can use the law," said Yu Wensheng, who was among those held.

He represents lawyer Wang Quanzhang, but says police have denied him access to his client and refused to say where he is being held.

A document police sent him last month shows Wang -- who has defended members of the banned religious group Falun Gong -- is accused of "inciting state subversion" and "picking quarrels and provoking troubles".

It adds he is being held under a form of "residential surveillance" where suspects can be held for up to six months incommunicado in unofficial jails.

"In a detention centre there are rules, and prosecutors are responsible. But with residential surveillance, it's just the police themselves," Yu said. "We suspect they are subject to torture."

- 'Rule of law' -

China's courts are tightly controlled by the Communist Party, with forced confessions often used as evidence and guilty verdicts delivered in more than 99.9 percent of criminal cases.

Over the past decade a small group of a few hundred lawyers, sometimes with official encouragement, used the courts to seek redress -- sometimes successfully -- for what they considered egregious rights violations.

They include victims of forced demolitions, illegal "black jails", dissidents jailed for their writing, and others detained for practising their religious faith.

Beijing law firm Fengrui, which has defended victims of sexual abuse, members of banned religious groups and dissident scholars, was at the centre of the crackdown with seven of its staff still held.

The firm courted publicity in a censored media environment, taking legal activism "to a new level", Eva Pils, a transnational law specialist at King's College London, told AFP.

"Basically what the party-state has been trying to do is make an example of them. It raises the question of whether the government thinks it really needs defence lawyers."

- 'Criminal gang' -

Fengrui founder Zhou Shifeng, who advised the families of children poisoned by milk powder in a 2008 scandal, was led away from a Beijing hotel with a hood over his head on July 10, a witness told AFP.

A week later state TV showed him "confessing guilt" under detention in a report which said he had "inappropriate relationships" with at least five women.

Broadcaster CCTV said the lawyers had tricked clients and "created a nuisance" in court by rowing with officials, making recordings and taking photographs. No official charges were mentioned.

The official news agency Xinhua has described the lawyers as a "criminal gang".

Yu said Fengrui stirred the Communist Party's greatest fear -- organised dissent -- by connecting "grassroots people" and activists, disturbing "the authorities' political bottom line".

At a key meeting in 2014 the party declared it was pursuing the "rule of law with Chinese characteristics", vowing to protect suspects' and lawyers rights' and create a fairer justice system to placate widespread anger over injustices.

But it also made clear that the ruling party -- which has tightened controls on dissent since Xi Jinping came to power -- would retain its supremacy over the legal system.

The detentions "make a mockery of President Xi Jinping's claims that China is governed by the rule of law," said Sophie Richardson, China director at campaign group Human Rights Watch.

- 'State security' -

The wife of Li Heping, who has defended dissident writers and environmental activists, watched helplessly as a crowd of police seized him at home, and he remains missing.

"There is no guarantee that he is safe," Wang Qiaoling told AFP.

"Lawyers are by definition people who say 'no'. The lawyers said 'no' to the situation facing people at the bottom of Chinese society, and they have been arrested for it."

Police have given the detained lawyers' attorneys indications their clients are probably being held somewhere in the northern port of Tianjin, and deny them access on grounds of "state security".

Faced with official obstruction, they have made freedom of information requests to police -- which have been sent back undelivered -- and attempted to take city authorities to court for abuse of power.

Still defiant, one of them, Tang Jitian, told AFP: "We try to make it as difficult as we can for the authorities, so they can't just treat these people as they wish."