JUBA (AFP) - At least one person has died in war-torn South Sudan of highly contagious cholera with several others infected, sparking concern for the more than 1.3 million people forced from their homes, the health minster said Thursday.

"There is an outbreak of cholera in the country.... the number is increasing," Health Minister Riek Gain told reporters, saying at least 19 cases of infection had been confirmed, one fatal.

While all cases reported have been in Juba's residential areas, it has raised fears for the huge numbers of people across the country surviving without proper shelter, clean water or toilets, having fled their homes during more than five months of civil war.

Over 79,000 civilians are sheltering in hugely overcrowded United Nations peacekeeping bases, including over 32,000 civilians crammed into UN camps in the capital alone.

Heavy rains are sweeping the impoverished country, hampering aid efforts and potentially exacerbating the spread of the disease.

Abdi Mohamed, World Health Organisation (WHO) chief in South Sudan, said those in UN camps had been vaccinated, but warned that did not guarantee 100 per cent safety.

Cholera is transmitted through drinking water or eating food contaminated with faeces or dirty hands.

After a short incubation period of two to five days, the disease causes severe diarrhoea, draining the body of its water. The dramatic loss of fluid is often fatal.

Juba's mayor Sarafino Wani promised "measures would be taken", including ensuring water sellers and restaurants take extra precautions so as not to spread the infection.

The UN and aid workers have warned of a growing humanitarian crisis in the young nation, including the risk of famine if rebel and government forces continue to fight.