Food prices are expected to rise rapidly in the next year because farmers are planting less as input costs escalate.

Thomas Malthus, the 18th-century cleric, must be chuckling in his grave. His grim prediction that humanity faced a future of rising food prices and mounting malnutrition has finally arrived.

The rising cost of food is a time bomb that could result in uprisings, African National Congress president Jacob Zuma told the World Economic Forum on Africa on Thursday.

A United Nations summit on the global food crisis asked rich nations on Wednesday to help "revolutionise" farming in Africa to produce more food for people facing hunger.