Famine threatens the lives of up to 5.5 million people in South Sudan, where droughts and flooding have destroyed crops and livestock, compounding "intense political instability", the UN said on Thursday.
The UN's World Food Programme said it needed $270 million (Dh991.7m) urgently to feed hungry South Sudanese in the first half of 2020 and avert mass starvation in the world's youngest country.
"Every factor is in place for there to be famine in 2020 unless we take immediate action to expand our deliveries in areas affected by floods and others affected by food loss," Matthew Hollingworth, the programme's country director, told Reuters.
"We need to pre-position food around the country in the next two to three months."
Mr Hollingworth said road access to many remote communities would be impossible after the rain season sets in.
The government declared a state of emergency in late October in Bahr El Ghazal, Greater Upper Nile and Greater Equatoria after months of flooding, the programme said.
Nearly 1 million people are directly affected by the floods and the water has not receded in many places, it said.
"The scale of the loss from the harvest is enormous," Mr Hollingworth said from Juba.
Fields with 73,000 tonnes of sorghum, millet and corn have been lost, as well as tens of thousands of cattle, chickens and goats on which families depended for survival, he said.
Acute malnutrition rates in children under the age of 5 have risen from 13 per cent in 2018 to 16 per cent this year, Mr Hollingworth said.
"They have gone above the global emergency threshold of 15 per cent," he said.
Water-borne diseases are spreading, although cholera has not been detected.
"It can only get worse because of the situation and environment people are living in," Mr Hollingworth said.
Civil war broke out in oil-producing South Sudan in 2013, less than two years after the country gained independence from Sudan following decades of war.
The conflict that has killed an estimated 400,000 people and forced millions from their homes.
Inter-communal fighting still occurs in pockets hit by the flooding, Mr Hollingworth said.
"Hunger and desperation bring instability when resources are stretched to the extent that makes an already unstable situation much worse," he said.
"It is a wake-up call for us all."