China has long held back the fact-finding mission led by Michelle Bachelet, focused on allegations of mass confinement, forced labour and compulsory birth control measures imposed on members of the Uighur, Kazakh and other Muslim minorities.

Chinese Foreign Ministry spokesman Wang Wenbin went on the offensive over such criticisms in Tuesday, saying "the US, Britain and other Western countries have been repeatedly staging political farces around the UN high commissioner for human rights' visit to China".

"They have first openly pressured and strongly demanded that the high commissioner visit China and Xinjiang, and conducted the so-called investigation with presumption of guilt," Wang said at a daily briefing.

The US, UK and other countries "jumped out and spared no effort to disrupt and sabotage the visit, creating conditions and obstacles for the visit," Wang said.

Chinese Foreign Minister Wang Yi met with Bachelet in the southern city of Guangzhou on Monday, telling her that China opposes "politicising" human rights and imposing double standards.

Bachelet's trip is the first to China by a UN high commissioner for human rights since 2005.

Her six-day visit is focused on allegations of abuses against Muslim minorities in the northwestern region of Xinjiang but rights groups fear it will help whitewash the crackdown labelled by the US as genocide.

China locked up an estimated million or more minorities in what critics describe as a campaign to obliterate their distinct cultural identities.

China says it has nothing to hide and welcomes all those without political bias to visit Xinjiang and view what it describes as a successful campaign to fight terrorism and restore order and ethnic cohesion.

From Guangzhou, Bachelet is to travel to Kashgar, once a stop on the Silk Road, and Urumqi, the Xinjiang capital.

The UN and China barred foreign media from accompanying Bachelet and it is unclear whom she will meet and how much access she will be granted throughout her visit.

The UN quoted Bachelet as telling Wang that she was looking forward to exchanges with "many different people during my visit, particularly with government officials, business leaders, academics, students and members of the civil society working on human rights and other social and economic issues".

"While we will be discussing sensitive and important issues, I hope this will help us to build confidence and enable us to work together in advancing human rights in China and globally," it quoted Bachelet as saying.

"Wang noted that to advance the international cause of human rights, we must first respect each other and refrain from politicising human rights," the Foreign Ministry said in a statement posted on its website.

"Multilateral human rights institutions should serve as a major venue for co-operation and dialogue rather than a new battlefield for division and confrontation," it said.

China's ruling Communist Party allows no political opposition and strictly limits free speech and rights to assembly and religious expression.

China is also one of the five veto-wielding permanent members of the UN Security Council and has signed but not ratified the International Covenant on Civil and Political Rights administered by Bachelet's office.

In an online meeting on Tuesday with Wang, German Foreign Minister Annalena Baerbock cited the "shocking reports and new evidence of very serious human rights violations in Xinjiang and called for a transparent investigation," her ministry said.

"Human rights are a fundamental part of the international order and Germany is committed to protecting them worldwide," Baerbock said.

"I think it's important that these accusations, which have been known for a long time, are addressed by the Chinese side, and I made that very, very clear in this morning's discussion," she added.

The US ambassador to the United Nations, Linda Thomas-Greenfield, echoed Baerbock.

She tweeted: "Horrified by the Xinjiang Police Files, which spotlight China's mass incarceration of Uyghurs and other ethnic and religious minorities."

Thomas-Greenfield also said that Bachelet and her office "must take a hard look at these faces and press Chinese officials for full, unfettered access - and answers".

Australian Associated Press