Life remains basic for many southern Sudanese
The number of people needing food aid in south Sudan has quadrupled in a year to more than four million, the UN's World Food Programme says.
The WFP wants to ensure the people have enough food to last until their next harvest in October.
Southern Sudan's agriculture minister Samson Kwaje blamed the surge on internal conflict and drought.
The region is recovering from a two-decade civil war and remains one of the least developed parts of the world.
Although the civil war with the north ended in 2005, some 2,500 people died in conflicts between rival communities in Southern Sudan last year - far more than in Darfur, the UN says.
Since the end of the war, millions of former refugees have returned home to start their lives again from scratch.
The BBC's Peter Martell, in the southern capital, Juba, says the situation in the region is grim.
And many in the south fear that tensions will rise further in the run-up to elections in April, our correspondent says, potentially putting even more people at risk.
The WFP is preparing thousands of tonnes of food to feed some of the millions it fears will be cut off when the rains start.
But the organisation also says it remains more than $480m (£300m) short of the food aid needed for Sudan.
Mr Kwaje - who said the WFP's figures represented half of the region's population - blamed the rising hunger on conflicts between rival ethnic groups.
But he also blamed incursions by the Lord's Resistance Army - a feared guerrilla army originally based in Uganda but now marauding across several countries.
The new WFP figures come from an annual assessment in which some 2,000 people across Southern Sudan were asked about what food they ate and where it came from.
The WFP's Leo van der Velden said: "This spike in the number of hungry people in Southern Sudan comes just ahead of the rainy season when roads become blocked and communities are cut off from food assistance."
As well as preparing for the first national multi-party elections in 24 years, Southern Sudan is also due to vote in an independence referendum next year.