JUBA, 04 December 2016 [Gurtong]-The country's hunger levels have doubled since last year, the UN agency said in a report released on Friday.
Nearly 60 per cent of the population of Northern Bahr el Ghazal State is affected, 56 per cent in Unity, and 47 per cent in Western Bahr el Ghazal.
"The scale of food insecurity remains unprecedented in South Sudan, despite seasonal improvements that are typical of the harvest season," WFP said.
The number facing severe hunger is expected to rise to 4.6 million between January and April next year, and increase even more from May to July unless aid is scaled up, it added.
"Food insecurity is anticipated to further deteriorate ... to the highest levels ever in the lean period, unless the humanitarian response is stepped up further to an unprecedented level," the UN agency said.
South Sudan descended into civil war in December 2013 when a row between President Salva Kiir and his sacked deputy, Riek Machar, ended with fighting that often erupted along ethnic fault lines.
A peace deal was signed in 2015 but violations have been frequent, and heavy fighting broke out again in July.
More than a million people have fled to neighbouring countries and another 1.87 million people are internally displaced.
The conflict has stopped farmers from reaching their farms in several parts of the country including the main food basket in the Greater Equatoria region, WFP said.
The fighting and tumbling oil production and prices have hammered South Sudan's economy.
Inflation has shot to 835 per cent in the year to October, while the official value of the pound has plummeted.
Conflict and insecurity have cut off trade routes and disrupted imports.
UN officials told Reuters on Thursday that attacks on aid workers and bureaucratic interference are preventing supplies from reaching tens of thousands of desperate South Sudanese who have fled their homes amid escalating violence.
Last month, the UN Food and Agriculture Organization said there was a growing "risk of famine" especially among the country's most vulnerable communities.