South Sudan is close to another famine, aid officials said on Monday, after more than four years of civil war and failed ceasefires in the world's youngest nation.

Almost two-thirds of the population will need food aid this year to stave off starvation and malnutrition as aid groups prepare for the "toughest year on record", members of a working group including South Sudanese and United Nations (UN) officials said.

“The situation is extremely fragile, and we are close to seeing another famine. The projections are stark. If we ignore them, we’ll be faced with a growing tragedy," said Serge Tissot, from the UN Food and Agriculture Organisation in South Sudan.

A total of 5.3-million people, 48 percent of the population, are already in "crisis" or "emergency" - stages three and four on a five point scale, according to a survey published by the working group.

The oil-rich east African nation has been torn apart by an ethnically charged civil war since late 2013, when troops loyal to President Salva Kiir and then-Vice President Riek Machar clashed.

Since then, more than 4-million people have been forced to flee their homes, creating Africa's larges refugee crisis since the 1994 Rwandan genocide.

The UN declared a famine in two districts in February, but said that crisis had started to ease in June last year.

“We are expecting to face the toughest year on record," UN Humanitarian Coordinator Alain Noudehou told a press conference in the South Sudanese capital Juba. Records for South Sudan began when it declared independence from Sudan in July, 2011.