The UN survey that suggests that five million Somalis face hunger (see earlier story) says that it is the more than one million people living in camps for those who have fled their homes that are the worst affected as they are the most vulnerable to disease.
More than 300,000 children under the age of five are severely malnourished and require immediate help.
The crisis follows poor rainfall in the south and central parts of Somalia where crop production has fallen by more than half in just six months.
Farmers have also lost many of their livestock in the recent drought.
Aid agencies have warned that the numbers could go higher if the Dadaab refugee camp in Kenya is closed down and thousands are forced to return to Somalia where they have no homes or livelihoods.
In January, aid agencies launched an appeal for more than $880m (£680m) to alleviate the humanitarian situation in Somalia but, so far, less than half of that sum has been donated.