It has been called a “perfect storm” - a combination of apparently unrelated events that have come together to trigger soaring food prices. Millions of people, particularly in developing countries, are affected by rises that have caused riots and many deaths.

Increased energy prices, competition between biofuels and food, rising demand from economic growth in emerging countries and the effects of sudden climatic shocks, such as drought and floods, have combined to cause skyrocketing prices in some of the world's poorest countries, such as Ethiopia and Burkina Faso.

Peter Smerdon, Africa spokesman for the UN's World Food Programme (WFP), told The Times: “The people hit hardest by this combination of factors are those living on the razor's edge of poverty.

There is not one single country in Africa not negatively affected. Indeed, most countries in the world are affected.”

The “perfect storm” has arrived as global food reserves are at their lowest for 30 years and commodity markets volatile and vulnerable to sudden spikes and speculation.

The situation is exacerbated by the falling value of the dollar, the currency in which all main commodities are traded.

In Sierra Leone, the price of rice has risen 300 per cent and in Senegal and much of the rest of West Africa by 50 per cent. Palm oil, sugar and flour, all imported, have also surged.

Two weeks ago Josette Sheran, the new US head of WFP, made an extraordinary emergency appeal for $500 million (£250 million) to 20 heads of government to offset the increased price of food commodities.

As ever, the world's poor - those who spend between 60 per cent and 80 per cent of their budget on food - are hit hardest. These groups include rural landless and small-scale farmers, but the biggest impact has been on the world's increasing urban poor.

Mr Smerdon added that, dangerously for governments, it is not a question of availability as one saw in previous drought-induced famines. “People can suddenly no longer afford the food they see on store shelves because prices are beyond their reach. It is about accessibility and it is hitting hard populations who are reliant on the markets.”

African governments are watching nervously. Food riots have been reported in recent weeks in several countries. At least 40 people were killed in protests in Cameroon in February. There have also been violent demonstrations in Ivory Coast, Mauritania, Senegal and Burkina Faso, where a nationwide strike against any more food price increases started yesterday.

Experts say that the only way out for Africa is greater self-sufficiency and alternative sources of energy to cut demand for imported food and oil. They praised an initiative by Sierra Leone to start producing rice from next year and to ban imported rice.

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