Almost eight million people in South Sudan, or two thirds of the population in the deeply-troubled country, are at risk of hunger, the United Nations warned in a report on Thursday.

One of the world's poorest nations, South Sudan has spent more than half of its life as a nation at war, with nearly 400,000 people dying during a five-year civil war that ended in 2018.

"Hunger and malnutrition are on the rise across the flood, drought, and conflict-affected areas of South Sudan, with some communities likely to face starvation if humanitarian assistance is not sustained and climate adaptation measures are not scaled-up," it said.

The joint report by the Food and Agriculture Organization, the UN children's fund UNICEF and the World Food Programme said the proportion of people facing high levels of food insecurity and malnourishment "is at the highest level ever", surpassing levels seen even during the conflict in 2013 and 2016.

It said 7.76 million people are likely to face acute food insecurity during the April-July 2023 lean season while 1.4 million children will be malnourished.

The report blamed a combination of conflict, poor macroeconomic conditions, extreme climate events, and spiraling costs of food and fuel as well as a decline in funding for humanitarian programmes.

"We’ve been in famine prevention mode all year and have staved off the worst outcomes, but this is not enough," Makena Walker, acting country director for WFP in South Sudan, said in a statement.

"South Sudan is on the frontlines of the climate crisis and day in, day out families are losing their homes, cattle, fields and hope to extreme weather," Walker said.

"Without humanitarian food assistance, millions more will find themselves in an increasingly dire situation and unable to provide even the most basic food for their families."

The world's youngest country has grappled with deadly conflict, natural disasters, economic malaise and relentless political infighting since it won independence from Sudan in 2011.

Famine was declared in South Sudan in 2017 in Leer and Mayendit counties in Unity State, areas that have often been a flashpoint for violence.

Last month, the UN's emergency response agency OCHA said around 909,000 people have reportedly been affected by flooding in South Sudan, as torrential rains ravage crops and destroy homes.