The United Nations refugee organisation says levels of malnutrition among children fleeing Somalia's drought could lead to a "human tragedy of unimaginable proportions".
The UNHCR says young children are dying on their way to or within a day of arrival at camps in Ethiopia and Kenya.
It estimates that a quarter of Somalis are either displaced within their country or living outside as refugees.
The worst drought in 60 years is being compounded by violence in south and central Somalia, the BBC reports.
The warning comes as aid agencies Oxfam, Save the Children and the Red Cross launch emergency appeals in response to the food crisis affecting more than 12 million people in the Horn of Africa. They are seeking a total of £93 million.
The UNHCR says the need for food, shelter, health services and other life saving aid is urgent and massive.