Some four million people in South Sudan are likely to face critical food shortages next month, British aid agencies have warned.
But the Disasters Emergency Committee says the cost of mounting an appeal to pay for aid might outweigh donations, according to the (BBC).
South Sudan's President has already warned of "one of worst famines ever".
More than a million people have fled their homes since fighting erupted between different factions of South Sudan's ruling party last December.
Thousands have now died in the conflict that started as a political dispute between South Sudan President Salva Kiir and Riek Machar, his sacked deputy, but escalated into ethnic violence.
The Disasters Emergency Committee (DEC) - which brings together 13 UK charities to deal with international crises - says it currently has less than half of the money it needs to "prevent the growing food crisis in South Sudan from turning into a catastrophe".
"If the conflict in South Sudan continues, and more aid cannot be delivered, then by August it is likely that some localised areas of South Sudan will slip into famine," the DEC says in its report, citing international food crisis experts.
The committee says the same experts helped predict the seriousness of the East Africa food crisis in 2011, which led to the first famine of the 21st Century in Somalia.
It predicts that responsive emergency work would cost 113 million pounds ($194 million), but to date they have only received 56 million pounds.
"We are very concerned... that despite some excellent news coverage of the situation, public awareness of the crisis in the UK remains very low, making a successful appeal extremely difficult," said DEC head Saleh Saeed.