One local authority warned that an epidemic of the deadly disease has "more or less begun already" in the besieged city.
The unidentified illness mainly affects the elderly and the under-14s and has been found in a region of South Sudan recently hit by extreme flooding.
The Yemeni Civil War, which began in 2015, has led to what could likely become the worst famine in a century.
Besides the tens of thousands killed and wounded, another million people are suffering from cholera in what the WHO called the largest epidemic of the disease in modern history.
The era of America as the U.N.'s sugar daddy is fast coming to an end.
At least 10,000 civilians have been killed in the Yemen conflict.
Yemen, South Sudan, Somalia, and Niger face famine. Syria, Iraq, Haiti, Mali, Ethiopia are suffering severe hunger.
People will continue to fall sick and die until the UN provides a comprehensive remedy for the travesty it caused.
Health officials are concerned that the disease is spreading as flood waters mix with sewage.
Many of Haiti's people are without drinking water and the spread of cholera is all but certain.
The U.N. has accepted partial responsibility in Haiti's 2010 cholera crisis.
The waterborne disease has killed more than 9,000 people since the earthquake in 2010.
An outbreak that has killed more than 8,300 people has been traced to U.N. peacekeepers