Human Rights Watch made the allegation in its annual report, launched in New York two days after executive director Kenneth Roth was barred from entering Hong Kong to release it there.

The NGO accuses President Xi Jinping's government of overseeing "the most brutal and pervasive oppression that China has seen for decades," including building a "nightmarish surveillance system" in Xinjiang province.

To fend off global efforts to hold it to account, Beijing has "significantly increased" efforts to undermine the international institutions created in the mid-20th century to defend human rights, HRW said.

"Beijing has long suppressed domestic critics. Now the Chinese government is trying to extend that censorship to the rest of the world," Roth said in the 652-page report.

"If not challenged, Beijing's actions portend a dystopian future in which no one is beyond the reach of Chinese censors, and an international human rights system so weakened that it no longer serves as a check on government repression," he added.

Roth was supposed to give a news conference this week in the semi-autonomous Chinese region of Hong Kong, which has been battered by nearly seven months of occasionally violent protests, in China's biggest political crisis in decades.

But the 64-year-old was turned back by authorities at the city's airport on Sunday.

Instead he launched HRW's World Report 2020, which reviews human rights practices in nearly 100 countries, at the United Nations headquarters.

The report accuses China of "repeatedly threatening other member states at the United Nations to protect its image and deflect discussion of its abuses."

It says that pressure has even reached the Secretary-General, Antonio Guterres, noting that he has been unwilling to publicly demand an end to the detention of Muslims in Xinjiang.

Trump, Modi, Bolsonaro

The report also says China, which has a permanent seat on the UN Security Council, routinely blocks initiatives at the world body's Human Rights Council.

Roth slammed western countries for falling to call China out, saying they had been "missing in action."

"Some leaders, such as US President Donald Trump, Indian Prime Minister Narendra Modi and Brazilian President Jair Bolsonaro, bridle at the same body of international human rights law that China undermines," he wrote.

Roth added that the European Union had been distracted by Brexit and handicapped by nationalist member states.

He highlighted China's penalizing of the NBA following a tweet from Houston Rockets general manager Daryl Morey backing the pro-democracy movement in Hong Kong last year as evidence of Beijing using its economic influence to intimidate critics.

HRW called for democracies to act together to counter Beijing's strategy, including offering alternatives to Chinese loans and freezing the assets of officials involved in the crackdown in Xinjiang.

It added that red-carpet treatment for Chinese officials should be conditioned on "real progress on human rights."

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