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At least 30,000 people are facing starvation in South Sudan, the UN has said, according to the BBC.
Three UN agencies warned that a famine could develop in southern Unity State, where fighting has prevented deliveries of humanitarian aid, the report says.
Two years of civil war have left nearly four million people - particularly young children - facing severe hunger, the UN said.
Both the government and rebel forces have accused each other of breaching a peace agreement signed in August.
The conflict has left a third of the country's population is in crisis, up 80% since last year, the UN's Food and Agriculture Organization (FAO), children's agency UNICEF and the World Food Program (WFP) said in a joint statement.
"People are on the edge of a catastrophe that can be prevented," said WFP chief Joyce Luma.
An official famine has not yet been declared, but almost a million people are described as living in a "catastrophic" situation, the highest level of food emergency under the Integrated Food Security Phase Classification (IPC), which classifies hunger on a scale of one to five.