Brics leaders met on Tuesday to plot the future course of the bloc of developing nations but divisions re-emerged ahead of a critical debate over a potential expansion of the group intended to boost its global clout.

Heightened tensions in the wake of the Ukraine war and Beijing's growing rivalry with the United States have pushed China and Russia - whose President Vladimir Putin will attend the meeting virtually - to seek to strengthen Brics.

They are seeking to use the August 22 to 24 summit in Johannesburg to forge the grouping, which also includes South Africa, Brazil and India, into a counterweight to Western dominance of global institutions.

"Right now, changes in the world, in our times, and in history are unfolding in ways like never before, bringing human society to a critical juncture," China's President Xi Jinping said in remarks delivered at a Brics business forum.

"The course of history will be shaped by the choices we make."

Xi skipped the event, despite the presence there of counterparts Cyril Ramaphosa of South Africa, Brazilian President Luiz Inacio Lula da Silva and India's Prime Minister Narendra Modi.

His remarks were delivered by Chinese Commerce Minister Wang Wentao, and it was not immediately clear why Xi, who had a meeting with host Ramaphosa earlier in the day, did not attend.

Comments from Brazil's Lula pointed to a divergence of vision within the bloc, which political analysts say has long struggled to form a coherent view of its role in the global order.

"We do not want to be a counterpoint to the G7, G20 or the United States," Brazil's Lula said on Tuesday during a social media broadcast from Johannesburg. "We just want to organise ourselves."

Beyond the enlargement question, boosting the use of member states' local currencies in trade and financial transactions to lessen dependency of the US dollar is also on the summit agenda.

"The objective, irreversible process of de-dollarization of our economic ties is gaining momentum," Russia's Putin said in a pre-recorded statement.

Russia's economy is grappling with Western sanctions over Moscow's war in Ukraine. Putin is wanted under an international arrest warrant for alleged war crimes in Ukraine, and is being represented at the summit by his foreign minister Sergei Lavrov.

South African organisers say there will be no discussions however of a common Brics currency, an idea floated by Brazil as an alternative to dollar-dependence.

POINT OF CONTENTION

Brics remains a disparate group, ranging from China, the world's second biggest economy, to South Africa, a relative minnow which is nonetheless Africa's most developed economy.

Russia is keen to show the West it still has friends but India has increasingly reached out to the West, as has Brazil under its new leader.

India and China have also periodically clashed along their disputed border, adding to the challenge of decision-making in a group that relies on consensus.

Speaking to reporters in Washington on Tuesday, White House national security advisor Jake Sullivan said he did not see Brics turning into a geopolitical rival of the United States.

"This is a very diverse collection of countries ... with differences of view on critical issues," he said.

Expansion has long been a goal of China, which hopes that broader membership will lend clout to a grouping already home to some 40% of the world's population and a quarter of global gross domestic product.

Russia is also keen to expand membership while South Africa's President Ramaphosa voiced support for the idea at the meeting with Xi.

The Brics leaders will hold a mini-retreat and dinner on Tuesday evening where they are likely to discuss a framework and criteria for admitting new countries.

India, which is wary of Chinese dominance and has warned against rushing expansion, has "positive intent and an open mind", Foreign Secretary Vinay Kwatra said on Monday. Brazil, meanwhile, is concerned that expanding Brics will dilute its influence, though Lula reiterated on Tuesday his desire to see neighbour Argentina join the bloc.

An Argentine government source involved in the country's negotiations to join Brics told Reuters that no new members were expected to be admitted to the bloc during the summit.

While a potential Brics enlargement remains up in the air, the grouping's pledge to become a champion of the developing world and offer an alternative to a world order dominated by wealthy Western nations is already finding resonance.

Over 40 countries have expressed interest in joining Brics, say South African officials. Of them, nearly two dozen have formally asked to be admitted, with some expected to send delegations to Johannesburg.