UNICEF's Yemen mission said that there had been an "alarming increase" in cholera-related deaths.
The International Committee of the Red Cross said Monday that 184 people had died of the disease since April 27, with 11,000 suspected cases across the country.
Cholera is a highly contagious bacterial infection spread through contaminated food or water.
Authorities in the capital, which is controlled by Iran- backed Huthi rebels, this week declared a state of emergency over the outbreak, the second wave of cholera cases in less than a year.
Hospitals are struggling to cope with the influx of patients.
Two years into a devastating war between the Huthis and government forces backed by a Saudi-led Arab military coalition, more than half the country's medical facilities are out of service.
Yemen's conflict has killed more than 8,000 people and wounded around 40,000, according to the WHO.
The UN has warned that two-thirds of the population is on the brink of famine.
The WHO now classifies Yemen as one of the worst humanitarian emergencies in the world alongside Syria, South Sudan, Nigeria and Iraq.