More than 500 people have succumbed to cholera and acute diarrhoea and left tens of thousands of others sick in Somalia since January, the United Nations said Thursday.

The UN's health agency said the epidemic had left more than 25,000 people sick, warning that number was likely to double by the end of June.

WHO put the number of deaths since the beginning of the year from the epidemic at 524, while the UN humanitarian agency OCHA said 533 people had died.

The case fatality rate, which measures the severity of an epidemic by defining the proportion of fatal cases within a specific timeframe, is currently 2.1 per cent - more than double the emergency threshold of one per cent.

OCHA spokesman Jens Laerke said the situation was particularly alarming in the Middle Juba and Bakool regions, where the case fatality rates have surged to 14.1 per cent and 5.1 per cent respectively.

The epidemic comes as the Horn of Africa country of 12 million people faces the threat of its third famine in 25 years of civil war and anarchy.

At least 260,000 people died in the 2011 famine in Somalia - half of them children under the age of five, according to the UN World Food Program.

Currently, 6.2 million people are in urgent need of humanitarian aid in Somalia, including 2.9 million who are facing "crisis or emergency levels of food insecurity", Laerke told reporters.

That means they are at levels three or four on a five-level scale, where level five is famine.