Africa's diamond trade has been severely hit by the downturn
Aid group Oxfam has told the BBC the G20 summit of world leaders must commit to a $580bn rescue package for Africa.
The group of the world's most powerful countries are meeting in the UK to discuss the global economic crisis.
Other international aid agencies have also expressed concerns that the needs of developing countries in Africa and elsewhere will be forgotten.
But UK minister Lord Malloch Brown has promised that Africa's needs will be addressed at the summit.
Speaking at an event at London's Chatham House think tank, he said the UK hoped a global plan for economic reform would include a package of assistance arranged through the International Monetary Fund and the World Bank.
Oxfam says Africa is looking for serious money and recognition that the crisis is hitting the poorest countries too.
"About $580bn (£403bn) we think is what is needed to service a stimulus in the African continent," Oxfam's regional manager in Kenya, Michael Obriane, told the BBC's Network Africa programme.
He also called for the world's richest countries to deliver on the promise to give 0.7% of their gross national income as aid and to crack down on tax havens.
bleed money from rich and poor countries alike, but particularly African countries," he said.
Oxfam's head of research, David Green, emphasised that Africa needs an increase in aid and more trade.
"You can't do a fiscal stimulus if you're an African economy, because you've no money," he told the BBC.
"One of the concerns at the moment is that 17 of the G20 countries have actually brought in various protectionist measures since the start of the crisis."
The aid agency has also called for reform of global governance, to give developing countries the same say as rich countries in decision-making at the global level
South Africa, which has so far avoided a recession, is the only African country in the G20.
But the BBC's Peter Biles in Johannesburg says economists are warning that up to 300,000 jobs could be lost this year, pushing South Africa's unemployment up from the current level of 22%.
The worst hit areas are in mining, the motor industry, clothing and textiles, he says.
In the neighbouring countries of Botswana and Namibia, production at some diamond mines has had to be suspended and some 200,000 jobs have been cut in the Democratic Republic of Congo's mining sector.