The WHO's Horn of Africa team said there had been 60,000 cases of cholera and acute watery diarrhoea (AWD) in south-central Somalia since January, with 75 percent of cases among children under five.
In November alone there were 6,300 cases, the WHO's Christian Lindmeier told journalists in Geneva.
Although endemic in Somalia, the last major outbreak of cholera was in 2007 and since then improved hygiene and sanitation had led to a drop in cases.
Massive population movements this year has increased the risk of diseases spreading, Lindmeier said.
Hundreds of thousands of Somalis have fled the country in search of refuge in neighbouring states amid the Horn of Africa's worst drought in decades.
Source: AFP