East Africa is in the midst of its worst drought in more than 60 years, with as many as 10 million people at risk.
The drought has led to crop failures and food shortages in parts of Ethiopia, Kenya, Djibouti and Somalia, and now a refugee crisis looms as people leave their homes to escape hunger.
The U.N. says thousands of Somalis are leaving their country, ending up in parched and overcrowded refugee camps.
Dadaab in Kenya is the world's largest refugee camp. Intended for 90,000 people, the U.N. says there are now more than 380,000 there.
And things look set to get worse. "All the predictions show seasonal rains are far away and the situation will deteriorate -- we have not even reached the peak of the crisis," said Dr. Unni Krishnan, disaster coordinator for children's development organization Plan International.
He says failed rains, high food prices and regional conflict have conspired to create a "deadly combination" for the region.
Rainfall in the Horn of Africa has declined steadily over the past 10 years, according to the U.N. World Food Program (WFP), but recent years have been especially dry.
"The rains just didn't come," said Judith Schuler, of the WFP in Ethiopia.
"Normally there are big rains in November-December and then again in the spring, but neither really came," she added.
"Farmers had to plant their seeds late and the rains that came were late and erratic and so heavy that seeds washed away."
She said the La Nina phenomenon and climate change had made the situation worse. "No one expects two consecutive failures of rainy seasons," Schuler said. "Droughts are coming more and more often."
With the next harvest not due until October, she added that food shortages are likely to get worse.
In Somalia, conflict has exacerbated the problem.
Valerie Amos, U.N. under-secretary for humanitarian affairs, said: "If you look at Somalia, where over 2.5 million people are affected, this is a country that's in the middle of a conflict, a country where the government doesn't control the whole of the country, where you have an organization Al-Shabab that controls a significant amount of the south and the center, so it's difficult to get in there and do long-term development."
Somalia has faced years of civil war between the country's makeshift government and Islamist fighters and Schuler said the instability in Somalia was making it hard for the WFP to deliver aid.
The al Qaeda-linked Al-Shabab group banned foreign aid organizations from operating in the country in 2009, accusing them of being anti Muslim.
But on Tuesday it announced it would lift the restrictions on foreign food agencies in drought-hit areas under its control.
Krishnan said rising food prices were also contributing to the crisis.
"From 2008 onwards we have seen a steady rise in food prices," he said. "In 2010 U.N. estimates show nearly 950 million were food insecure."
The WFP says food prices in the Horn of Africa are still inflated and crop failures have only increased prices in the desperately poor region.
Schuler said the WFP is already providing food assistance to six million people in the region, and that will increase in coming months.
Humanitarian groups such as Save the Children and Oxfam have launched fund-raising appeals but Krishnan said more can be done.
"Unfortunately, this is a disaster that hasn't had much attention from the international community or donors," he said.
He added: "There is a feeling that, 'those things happen in that part of the world, so what is new about it?' But this is an unprecedented situation that has been slowly building up and has reached a flash point now.
"But if we act now we will be able to avert perhaps one of the worst humanitarian crises in the region."
Isha Sesay, Michael Holmes and Elise Labott contributed to this report.