China on Wednesday dismissed Washington's allegation that Beijing was committing genocide against Uighurs and other minorities as "outrageous lies" and "poison" in a rancourous epilogue to a combative period in relations between the superpowers.

Under the administration of outgoing President Donald Trump, the US has butted heads with China over trade, security, technology, the origins of the Covid-19 pandemic and rights from Hong Kong to Xinjiang, home to the Uighur minority.

In the dying days of Trump's administration, Secretary of State Mike Pompeo launched his final broadsides against China.

America's top diplomat said Beijing's sweeping incarceration of mostly Muslim minorities in the far western Xinjiang region amounted to genocide and crimes against humanity.

"We are witnessing the systematic attempt to destroy Uighurs by the Chinese party-state," Pompeo said on Tuesday.

In a rebuttal typifying the strained language between the rivals, a foreign ministry spokeswoman in Beijing hit back on Wednesday, accusing Pompeo of fabricating "sensational false propositions" throughout his term in office.

Genocide had "never happened in the past, is not happening now and will never happen in China," spokeswoman Hua Chunying said in her last public joust with Pompeo, a regular target of the ministry's anger throughout the Trump administration.

Rights groups say at least one million Uighurs and other Turkic-speaking Muslims have been incarcerated in camps in Xinjiang.

Independent access to the sensitive area is highly restricted, making reporting and verification of the allegations near impossible.

China accused outgoing US Secretary of State Mike Pompeo of "outrageous lies" for saying Beijing was carrying a genocide against Uighurs
China accused outgoing US Secretary of State Mike Pompeo of "outrageous lies" for saying Beijing was carrying a genocide against Uighurs POOL / Andrew Harnik

But witnesses and activists say that China is seeking to forcibly integrate the Uighurs into the majority Han culture by eradicating Islamic customs, including by forcing Muslims to eat pork and drink alcohol -- both forbidden by their faith - whilst imposing a regime of effective forced labour.

Pompeo's vociferous criticism of Beijing has been a hallmark of his tenure, but he had earlier danced around directly alleging genocide -- although he repeatedly stated his view the treatment of Uighurs was reminiscent of Nazi Germany's policies.

Pompeo urged all international bodies including courts to take up cases over China's treatment of the Uighurs and voiced confidence that the United States would keep raising pressure.

China denies wrongdoing and contends that its camps are vocational training centres meant to reduce the allure of Islamic extremism in the wake of attacks.

Pompeo's successor, President-Elect Joe Biden's pick for Secretary of State Antony Blinken, said Tuesday that he agreed with the incumbent's decision to label China's actions as genocide.

Blinken has also vowed to stay tough on China, echoing other members of the incoming administration who have said they will continue to fight against Chinese trade practices and threats to US security.

But Hua saved most of her criticism on Wednesday for Pompeo, calling him a "clown" and instead suggesting that other US officials had been misled by members of the Trump administration.

Hua said she hoped the incoming Biden administration, which takes over on Wednesday, would "treat China objectively and rationally and meet China in the middle."

Biden is expected to be more measured in tone and knit back together tattered alliances on the global stage.

But he has told US media that he will keep Donald Trump's trade war tariffs on China for the time being when he moves into the Oval Office.