The comments come after US President Donald Trump unveiled plans for his new "Board of Peace" at the World Economic Forum.

Although originally meant to oversee Gaza's rebuilding, the board's charter does not seem to limit its role to the Palestinian territory and has sparked concerns Trump wants to rival the United Nations.

While China and Brazil have both been invited to join Trump's new grouping, neither has confirmed participation.

Xi told Lula during their Friday morning phone call that in the current "tumultuous" international situation, China and Brazil "are constructive forces in maintaining world peace and stability", according to a readout published by state broadcaster CCTV.

"They should stand firmly on the right side of history... and jointly uphold the central role of the United Nations and international fairness and justice," Xi said.

European leaders have expressed doubts over Trump's norm-busting proposal, with some viewing it as an attempt to potentially sideline or even replace the United Nations.

While in Davos, Switzerland, Trump said that once complete, the board "can do pretty much whatever we want", while adding that "we'll do it in conjunction with the United Nations".

Beijing's foreign ministry said on Wednesday that "no matter how the international situation changes, China firmly upholds the international system with the United Nations at its core".

Brazil has also expressed scepticism about the Board of Peace, saying it could represent "a revocation" of the United Nations.

Lula's special advisor Celso Amorim told Brazilian media that "we cannot consider a reform of the UN made by one country."

During Trump's global tariff onslaught last year, China and Brazil sought to present their countries as staunch defenders of the multilateral trading system.

Xi told Lula in August they could set an example of "self-reliance" for emerging powers.

China, a permanent member of the UN Security Council, engages with the international body even as it has objected to what it terms internal interference.

Advocacy groups like Human Rights Watch have accused China of seeking to undermine the United Nations by reducing contributions to the organisation's rights budgets, establishing an alternative international mediation body and blocking activists from UN events.