Two major aid agencies have launched $10m (£6.7m) appeals for drought-stricken Niger in West Africa.
About seven million people - half of the country's population - face food shortages after crop failures last year.
Aid organisations Oxfam and Save The Children say the situation is growing more critical by the day.
Their concern is shared by the UN, which says the crisis is of a magnitude not seen before.
Save the Children says 400,000 children under five are at risk of starvation.
Oxfam says it will focus help towards a further two million adults who are facing severe food shortages.
The crisis, in the world's most under-developed nation, has been caused by a combination of a crop failure - following a drought last year - along with big increases in the price of many staple foods.
The UN's country director, Khardiata Lo Ndiaye, says the emergency is already worse than the drought in 2005, and says that help is needed quickly.
"The magnitude of this crisis has not been seen before. We need money now!" she said.
The UN currently only has just over half the funds it has appealed for to support the population until the next harvest, which is due in September.