Children under 5 comprise 13 percent of the cases, UNICEF said, adding that funding is needed as the agency has been using its flexible internal resources to meet critical needs.
In addition to Juba, cholera cases have also been reported in Bor, Jonglei state, as well as Torit in the state of Eastern Equatoria.
Last year a cholera outbreak in South Sudan infected more than 6,000 people and killed 167, according to World Health Organization figures.
Cholera is a fast-developing, highly contagious infection that causes diarrhea, leading to severe dehydration and possible death.
South Sudan’s cholera outbreak intensifies the humanitarian needs of a poor country facing a violent conflict that has displaced more than 2 million people as government troops try to put down a rebellion.
Amid the civil war, many civilians — especially children — are at risk.
More than 63,000 children have been admitted by UNICEF for treatment of “severe acute malnutrition” so far in 2015.