The move comes as emerging economies across the world have been hit by speculation that US may scale back its key economic stimulus programme soon.

That has seen investors pull out money, hurting currencies of emerging nations.

The Brics leaders said the details of the fund were still being worked out.

"The initiative to establish a Brics currency reserve pool is at its final stage," Russian President Vladimir Putin said during the G20 summit in St Petersburg.

"Its capital volume has been agreed at $100bn," he added.

The chairman of the US Federal Reserve, Ben Bernanke, said in May that the US might start to rein back on its $85bn-a-month bond-buying programme.

The programme was introduced with the aim of increasing liquidity in the markets after the global financial crisis. Part of the increased cash has flowed into emerging markets, helping to lift asset prices there.

But Mr Bernanke's statement, coupled with a recovery in the US economy, has seen investors pull out money from these economies.

They have been rushing to buy dollars in anticipation of higher returns.

That has resulted in volatility in the stock markets and currencies of these nations - triggering concerns about the impact of such moves on the overall growth.

Against the US dollar, the Indian rupee has weakened 24%, South Africa's rand nearly 17%, Brazilian's real 15% and Russia's rouble 8% since May.

China's yuan - which is traded within 1% of the daily rate set by the country's central bank - has strengthened slightly.

The latest move to establish the fund is being seen an attempt by Brics nations to tackle any potential volatile movements in their currencies.

China will contribute $41bn to the pool, with Brazil, India and Russia putting in $18bn each and South Africa $5bn.

Earlier this year, Brics nations discussed the formation of a new development bank to fund infrastructure and development projects throughout the developing nations.