Aid agencies warned Sunday that starvation and diseases like malaria and cholera were set to intensify the crisis in South Sudan, which has been devastated by six months of conflict.
War in the young nation has already killed thousands and forced more than 1.5 million people from their homes, and aid agencies warn of the risk of famine should fighting continue.
"The conflict has taken thousands of lives and destroyed the livelihoods of millions," Oxfam’s South Sudan chief Emma Jane Drew said Sunday.
"The people of South Sudan have been exposed to a triple crisis -- conflict, hunger and disease -- and with the rains now in full swing, the situation only stands to deteriorate."
On Saturday, the United Nations launched an appeal for funds, begging for over a billion dollars to support almost four million people hit by the fighting.
"Now that the rains have set in, conditions in South Sudan are deteriorating by the day: people are literally living in mud," UN aid chief for South Sudan Toby Lanzer said Saturday.
"Cholera has broken out, malaria is rampant and many children are malnourished. Millions of people need emergency healthcare, food, clean water, proper sanitation and shelter to make it through the year."
President Salva Kiir and his arch-rival Riek Machar committed themselves again this week to a ceasefire, although many analysts are sceptical they really want a negotiated end to the conflict, and instead believe a military victory is still possible.
Two earlier ceasefire deals were broken within hours.
"If we are to avoid a famine in South Sudan, the time to act is now," Oxfam added.
Months of dragging peace talks in Ethiopia have made little progress, so far costing over 17 million dollars (12 million euros).
"Both parties to the conflict must genuinely commit to building a path to peace that is robust and enduring, and they must call on their troops to lay down their arms and stop putting the lives of their own citizens at risk," Oxfam added.
Fighting broke out on December 15, pitting government troops against militia forces loosely loyal to Machar.
The violence has taken on a complex ethnic dimension, with the Dinka people of Kiir fighting the Nuer, Machar's tribe.