BRICS' five developing nations are set to admit Saudi Arabia, Iran, Ethiopia, Egypt, Argentina and the United Arab Emirates in a move aimed at growing the clout of the bloc as it pushes to rebalance the prevailing world order.
The expansion could also pave the way for dozens more countries to seek admission to the grouping, which has pledged to address their grievances over a world order many feel is rigged against them.
BRICS - whose acronym was originally coined by an economist at Goldman Sachs - currently comprises Brazil, Russia, India, China and South Africa.
Deepening geopolitical polarisation in the wake of Russia's invasion of Ukraine and China's declining relations with the United States are spurring efforts by Beijing and Moscow to forge BRICS into a viable counterweight to the West.
"BRICS has embarked on a new chapter in its effort to build a world that is fair, a world that is just, a world that is also inclusive and prosperous," South African President Cyril Ramaphosa said.
Ramaphosa, who is hosting the three-day BRICS leaders' summit in Johannesburg, said the six candidate countries would formally become members on January 1, 2024.
Ramaphosa and Brazilian President Luiz Inacio Lula da Silva left the door open to the possibility of admitting other countries in the future.
"We have consensus on the first phase of this expansion process and other phases will follow," Ramaphosa told reporters on Thursday.
Lula said globalisation's promises had failed and it was time to revitalise co-operation with developing countries as "there is a risk of nuclear war" - an apparent allusion to growing tensions between Russia and the West over the Ukraine conflict.
United Arab Emirates President Mohammed bin Zayed, whose country is already a shareholder of the bloc's New Development Bank, said he appreciated his country's inclusion in the expansion.
Ethiopian Prime Minister Abiy Ahmed called the BRICS leaders' decision to invite his country to join "a great moment".
In a reflection of the bloc's growing influence, United Nations Secretary-General Antonio Guterres attended Thursday's expansion announcement.
He echoed a recurring plea by BRICS for reforms of institutions such as the UN Security Council, the International Monetary Fund and World Bank, stating that global governance structures "reflect yesterday's world".
"For multilateral institutions to remain truly universal, they must reform to reflect today's power and economic realities," he said.
"In the absence of such reform, fragmentation is inevitable."
The debate over enlargement has topped the summit agenda.
While all BRICS members publicly expressed support for growing the bloc, there were divisions among the leaders over how much and how quickly.
Despite being home to about 40 per cent of the world's population and a quarter of global gross domestic product, BRICS members' failure to settle on a coherent vision for the bloc has long left it punching below its weight as a global political and economic player.
"This membership expansion is historic," China's President Xi Jinping said in remarks following the announcement on enlargement.
"It shows the determination of BRICS countries for unity and co-operation with the broader developing countries."
More than 40 countries have expressed interest in joining BRICS, South African officials said, and 22 have formally asked to be admitted.
They represent a disparate pool of potential candidates motivated largely by a desire to level a global playing field, attracted by BRICS' promise to rebalance world bodies dominated by the US and other wealthy Western states.
Indian Prime Minister Narendra Modi said the bloc's expansion should be an example to other global institutions.
"The expansion and modernisation of BRICS is a message that all institutions in the world need to mould themselves according to changing times," he said.