Death toll from cholera outbreak in southern Sudan has risen to 516, infecting 13,852 others in the past four months and the water-borne disease is spreading, the World Health Organization (WHO) warned on Thursday.

In a statement, the UN health agency said the most affected areas, in the town of Yei, which borders Uganda, and the vast region's main city of southern Sudan Juba have been the most severely affected areas.

However, the WHO said the outbreak of cholera in the cities of Juba and Yei is stabilizing with the number of cases decreasing.

"As of May 6, the cumulative number of cases in southern Sudan is 13,852, with 516 deaths," WHO said in the statement.

"Six out of ten states have confirmed cases. The current focus of the outbreak is in East Equatoria State," the UN health agency added.

It said several cases and deaths, however, were reported in locations outside Yei and Juba.

Control measures, including strengthening surveillance and reporting systems, improving case management and water chlorination were continuing.

"A task force including key partners (WHO and other UN agencies, NGOs) is assisting the Ministry of Health of Southern Sudan to coordinate the response to the outbreak," the statement said.

Cholera, an acute intestinal infection spread by contaminated water or food, causes vomiting and acute diarrhoea that can lead to dehydration and death within 24 hours.

It is a highly contagious and potentially fatal disease that thrives in places with poor hygiene and inadequate water supplies.

WHO and other aid agencies are helping Sudanese authorities by providing antibiotics and chlorination tablets.

International aid agencies have warned that an increase in the number of returnees following the signing of peace agreement and an onset of the rainy season could spark further spread of cholera in the southern Sudan.

The first news of the outbreak came in late January with three deaths and 48 patients admitted in local health facilities.