Members of the United Nations Security Council (UNSC) have described the current food insecurity situation in South Sudan as the “worst in the world”.

Nearly a million children aged under five face acute malnutrition, the World Food Programme (WFP) and UN children's agency UNICEF said in a joint statement released late Friday, after their top directors visited the impoverished nation.

"They fear the world is allowing a repeat of what occurred in Somalia and the Horn of Africa just three years ago; when early warnings of extreme hunger and escalating malnutrition went largely unheeded until official famine levels were announced," the statement read.

UN warns of ‘hunger catastrophe’ for South Sudanese children

Without swift action, 50,000 children could die from malnutrition this year, they added.

"The world should not wait for a famine to be announced while children here are dying each and every day," top UNICEF director Anthony Lake said.

The UN Security Council said Friday the food crisis is now the worst in the world, as it called on countries who had pledged 618 million dollars in aid to make good on their promises.

Thousands have been killed and over 1.5 million people have fled more than seven months of fighting between government troops, mutinous soldiers and ragtag militia forces divided by tribe.

Threat of Famine Looms in South Sudan

"If we are to rapidly expand our operations and save more lives, then we need more resources, and the international community has to act now," WFP chief Ertharin Cousin said.

A third of the population, nearly four million people, face "dangerous levels" of hunger, the UN says.

Fighting broke out in December, sparked by a power struggle between President Salva Kiir and his sacked deputy Riek Machar.

Top UN aid chief John Ging has called it a "man made problem, the result of a political disagreement between two powerful individuals."