A lack of rain, ongoing economic crisis and years of civil war are being blamed for the worsening situation.
The report stopped short of declaring a famine, but says nearly two million people go without food for long periods and suffer acute malnutrition, leading to many deaths.
Over the past two years, the number of people needing food aid has increased by two million.
If the lack of rain and poor harvests continues, 21,000 people could suffer from famine.
What should be done to stop this disaster?
Presenter: Adrian Finighan
Pierre Vauthier – deputy representative of the UN’s food and agricultural organisation in South Sudan
Alan Boswell – senior analyst at the International Crisis Group
Jok Madut Jok – cofounder of the Sudd Institute