The number of suspected cholera cases in Yemen has now exceeded 200,000, the United Nations says.
The joint statement by Unicef and the World Health Organization said the country was now facing the worst cholera outbreak anywhere in the world.
The two UN agencies say they are doing everything they can to stop the outbreak from accelerating.
So far more than 1,300 people have died – one quarter of them children – with the death toll expected to rise.
“In just two months, cholera has spread to almost every governorate of this war-torn country,” the statement says, with an estimated 5,000 new cases every day.
Yemen’s health, water and sanitation systems are collapsing after two years of war between government forces and the rebel Houthi movement.
Hospitals are overcrowded and severe food shortages have led to widespread malnutrition, making Yemenis – especially children – even more vulnerable to cholera.
The UN says it is deploying rapid-response teams to go house-to-house telling people how to protect themselves by cleaning and storing drinking water. But clean water is in short supply.
Cholera is an acute diarrhoeal infection caused by ingestion of food or water contaminated with the bacterium Vibrio cholera.
Most of those infected will have no or mild symptoms but, in severe cases, the disease can kill within hours if left untreated.
The war has left 18.8 million of Yemen’s 28 million people needing humanitarian assistance and almost seven million on the brink of famine.