President Joe Biden's nominee to be US ambassador to China, Nicholas Burns, took a tough line on dealings with China at his Senate confirmation hearing on Wednesday, saying "genocide in Xinjiang," abuses in Tibet and bullying of Taiwan must stop.

Human rights advocates and the US government have termed China's treatment of Uyghur Muslims in its Xinjiang region "genocide," a characterization that China rejects.

Burns, 65, a career diplomat and former US ambassador to NATO, also said Washington is correct in adhering to its "one China" policy on Taiwan, but also right to oppose actions from Beijing that undermine the status quo and that the United States has "enormous latitude" to deepen security assistance.

"The administration and Congress should help Taiwan 'to maintain a sufficient self-defense capability,' as the Taiwan Relations Act clearly states," Burns told the Senate Foreign Relations Committee.

He said the United States cannot trust China to meet commitments it has made on Taiwan, and that Washington has "enormous latitude" to deepen its security assistance to the island.

Burns is not expected to face significant opposition as nominee for the high-profile post. The desire for a hard line in dealings with China is one of the few truly bipartisan sentiments in the deeply divided US Congress, and Burns stressed the importance of pushing back against Beijing on trade, human rights and other issues.

He won praise from both sides of the aisle. "It is, I think, appropriate that Ambassador Burns was appointed to this position," said Senator Jim Risch, the ranking Republican on the committee.

Burns also discussed at some length his view that China is relatively isolated internationally.

"The Chinese are being so aggressive, they have stirred up a lot of opposition to them. And I think we ought not to exaggerate their strengths, or underestimate the strengths of the United States," Burns said.

Burns also said Beijing has been "stonewalling" the world about the origins of the coronavirus vaccine.