The United Nations World Food Programme (WFP) is asking donor countries to fund an expanded aid operation in Zimbabwe.
Food shortages have become common in Zimbabwe
The WFP says a poor harvest and the country's worsening economic situation means hundreds of thousands of Zimbabweans are running out of food.
It says it will have to provide assistance to more than three million people over the coming months.
Without additional funds, UN food stocks will be completely exhausted by the end of 2007, the agency says.
According to the WFP an estimated 3.3 million people will need assistance during the peak hunger period between November and March.
It has appealed for $118 million dollars (£58 million) in aid from international donors.
"WFP plans to feed more than 10 times the current number of beneficiaries over the next eight months to avert the threat of widespread hunger, but to do this we need more donations and we need them immediately," the agency's regional director, Amir Abdulla, said.
Some of the communities worst-affected are in Zimbabwe's drought-hit southern provinces.
But the UN says the situation has been made worse by soaring poverty, hyper-inflation and the impact of HIV/Aids.
The BBC's correspondent, Peter Biles, says the economic crisis in Zimbabwe is causing increasing hardship, and government price controls have led to panic buying and severe shortages of many basic food items in the shops.
The WFP said Zimbabweans would be forced to take desperate measures if no additional help was given.
"Vulnerable families will be forced to adopt risky survival measures, including eating potentially poisonous wild foods, selling their remaining household assets, exchanging sex for food and crossing illegally into South Africa," the agency said.