China's muzzling of lawyers, labour activists, journalists and gender campaigners amounts to a systematic attempt to choke off civil society, an effort that took on new seriousness last year, said the authors of a new report on human rights in the world's second most powerful economic power.

Under the leadership of President Xi Jinping, China has criminally detained hundreds of people involved in defending human rights. Many have been deprived of rights to a lawyer and fair trial, and their treatment has been marred by an "alarming prevalence of torture to force confessions," said the 2016 annual report by Chinese Human Rights Defenders, an advocacy coalition of non-governmental organizations.

Security laws and rules for overseas NGOs that came into force last year give the Chinese state "draconian" new powers to "expand already strict control over independent organizations, including their funding sources, staffing, and activities," the report states.

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Mr. Xi and his administration "are really intent on shutting off any avenue for civil society to participate in the improvement of the Chinese nation," said Frances Eve, a researcher for Chinese Human Rights Defenders. Groups seeking to combat corruption, uphold Chinese law and improve the treatment of women have all been targeted, even though the Communist Party itself has said it is seeking improvements in each of those areas.

"The government is saying, 'you're not allowed to participate. This is something that only we the Communist Party can do,' " Ms. Eve said. "And not only are they not letting people participate, but they're criminalizing activities to take part in public participation in governance and social issues."

Chinese authorities have waged a public campaign against what they have called foreign and hostile forces, accusing the U.S. in particular of funnelling money into China to foment unrest and destabilize society in the name of undermining the Communist Party.

Critics say China has used that argument to justify the most rigorous crackdown in decades, one "aimed at the suppression of civil society from all sides," said human-rights lawyer Li Fangping.

Last summer, four lawyers and activists campaigners were put through hours-long trials, in which they confessed to fomenting "colour revolution" and trying to overthrow the Communist Party. They were convicted of "subversion of state power," an unusually serious charge that has only recently begun to be used against those, such as lawyer Zhou Shifeng, who sought justice for victims of a contaminated baby formula scandal.

Mr. Zhou, according to state media reports of the verdict against him, had "hired protesters to disturb the judicial system" and "attempted to manipulate public opinion and damage national security by spreading subversive thoughts."

The Chinese constitution says citizens "enjoy freedom of speech, of the press, of assembly, of association, of procession and of demonstration."

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In total last year, Chinese courts convicted six people for subversion of state power and 10 for inciting subversion of state power.

Local human-rights lawyers have suffered "a huge blow, including restricted freedoms, some people were detained and arrested, some placed in long-term detention and there are even allegations that torture has been used," Mr. Li said.

One detained lawyer, Xie Yang, in January described an interrogator telling him: "I'm going to torment you until you go insane." Activist Xie Fengxia in late 2015 said he was forced to spend more than 100 hours with his arms and legs shackled together.

Activists and lawyers routinely disappear for months, in violation of Chinese standards for prompt notification of families. Authorities have refused proper medical treatment to some. A series of dissidents have been placed on television to deliver confessions that critics say appear scripted and coerced. Others have been pressured to dismiss their own lawyers in favour of government-appointed counsel; the report documents 15 cases in 2016.

Authorities, however, have said they treated human-rights lawyers according to the law, in an effort to prevent conspiracies that could drag China into chaos.

A militaristic video posted to the website of the Chinese Supreme People's Court last summer features images of war and dead refugee children. "If one day China turned into what it looks like in Iraq, Syria, Ukraine, Turkey, what will our children suffer?" says the video, which has been watched more than 17 million times.

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It lists dissident leaders and human-rights lawyers as "agents of Western powers."

"They are destroying China's domestic stability and harmony with all possible means."