Leaders of the Brics nations - Brazil, Russia, India, China and South Africa - are due to open a summit in Johannesburg on Tuesday where they will weigh expanding membership as some members push to forge the bloc into a counterweight to the West.

Heightened global tensions provoked by the Ukraine war and a growing rivalry between China and the United States have added urgency to a drive to strengthen the bloc, which has at times suffered from internal divisions and a lack of coherent vision.

"An expanded Brics will represent a diverse group of nations with different political systems that share a common desire to have a more balanced global order," South Africa's president, Cyril Ramaphosa, said in an address ahead of the meetings.

Boosting the use of member states' local currencies is also on the agenda. South African summit organisers, however, say there will be no discussions of a Brics currency, an idea floated by Brazil earlier this year as an alternative to dollar-dependence.

Ramaphosa will host Chinese President Xi Jinping, Brazil's Luiz Inacio Lula da Silva and Indian Prime Minister Narendra Modi from August 22 to 24.

Russian President Vladimir Putin, wanted under an international arrest warrant for alleged war crimes in Ukraine, will not travel to South Africa and instead join virtually.

Expansion has long been a goal of bloc heavyweight 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 GDP.

The 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.

But expansion has become a point of contention.

Russia is keen to bring in new members to counter its diplomatic isolation over its invasion of Ukraine. South Africa has also voiced support.

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 growing Brics will dilute its influence.

While a potential Brics enlargement remains up in the air, the bloc's pledge to become a champion of the developing "Global South" 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.