More than 10 million people need food aid after crop failure in six southern African countries, the United Nations food agency says.
Aids is reducing harvests across southern Africa
The World Food Programme says that people are going hungry after erratic weather, made worse by problems with fertiliser and seeds in some countries.
Zimbabwe and Malawi are the worst hit countries, the WFP says.
It urged donors to send aid to "avoid widespread hunger from developing into a humanitarian disaster".
Malawi has experienced its lowest maize harvest since 1992 and will only cover 37% of average national consumption of 3.4m tonnes of cereal, the WFP said.
In Zimbabwe, the WFP says that four million people may need aid in the coming year.
Swaziland, Mozambique, Zambia and Lesotho will also need help, it said on the basis of new crop studies.
All countries are badly hit by the Aids pandemic, which kills those who would normally be the most productive farmers.
Donors say that Zimbabwe's problems have been made worse by the government's seizure of white-owned farms.
This is strongly denied by the government.