At least 15 million South Africans face food shortages after a severe drought.
Food rations in neighbouring Zimbabwe have been halved
Director for Disaster Intervention Toffee Mokgethi told the BBC the government would have to provide emergency food supplies by June.
Farmers' leaders say the current drought is possibly the worst to hit the country in nearly a century.
South Africa will have to use its large food reserves to feed itself, sharply reducing its capacity to send relief to other countries in the region.
Ms Mokgethi said the drought had wiped out most of the grain harvest in rural areas.
"You travel across the country and you see nothing," she said. "Most fields are... just laying there."
Officials are planning to provide supplies to people affected, she said.
Farmers' leaders say the situation has been made worse by a rise in the market price of the staple maize crop, on which the poor depend.
UN agencies are no longer purchasing maize from South Africa, turning to American and Canadian imports instead.
The BBC's Martin Plaut says South Africa has large food reserves so it is not a question of importing food.
But the same cannot be said of the rest of southern Africa, he adds.
The World Food Programme is feeding 4.5 million people in southern Africa, mainly in Zimbabwe. Many have had their meagre rations reduced and are living on half-rations.
Lesotho has lost almost all of its crop while Swaziland, Malawi and parts of Mozambique are also affected by drought.