More than 200,000 suspected cases of cholera have been recorded in the Arabian Peninsula country and as many as 300,000 people could become infected by the end of August, Margaret Chan, WHO's director-general, said in a statement on Saturday.
"In just two months, cholera has spread to almost every governorate of this war-torn country," Chan and Anthony Lake, executive director of UNICEF, the UN children's agency, said.
"Already more than 1,300 people have died - one quarter of them children - and the death toll is expected to rise."
Cholera is a highly contagious bacterial infection spread through contaminated food or water. It can be fatal within hours if left untreated.
Although the disease is easily treatable, doing so in Yemen, a country riven by conflict, has proved particularly difficult.
The UN has placed blame on all the rival sides and their international backers for the spread of cholera, which it calls a man-made humanitarian catastrophe.
"This is because of conflict. It's man-made, it's very severe. The numbers are absolutely staggering. It's getting worse," Stephen O'Brien, a senior UN humanitarian affairs official, said.
"The cholera element, in addition to all the lack of food, the lack of medical supplies ... one has to put that at the door of all parties to the conflict."
|More than 1,300 people have died since the cholera outbreak began in April [Abduljabbar Zeyad/Reuters]|
Two years of conflict have killed more than 10,000 people, wounded 45,000 others, and displaced more than 11 percent of the country's 26 million people.
On Friday, the humanitarian group Oxfam called for a ceasefire because of the outbreak, but the war shows no sign of letting up.
At the Sabeen hospital in the capital, Sanaa, two to three new patients arrive every minute, with many suffering from cholera.
The outbreak began last year, but a second wave of the waterborne disease has spread even faster in the past two months.
"We are receiving many patients from all over the country, and some are in bad condition," Ismail Mansouri, a physician, said.
"We are facing many obstacles. We lack medical equipment, rehydration solutions and medicine."
The hospital does not have enough doctors and nurses, Mansouri said.
Those who are there have been working around the clock to deal with the crisis.
Because of the war, many Yemenis face difficulties accessing clean water.
A large number of patients also have difficulty reaching the closest medical facility.
Some patients had to travel for hours just to reach the Sabeen hospital.
UNICEF also called for all sides of the conflict to allow aid agencies better access to those in need.
"The number of cases is increasing at a staggering rate," Najwa Mekki, UNICEF spokesperson, told Al Jazeera.
"It's critical that aid agencies and others are able to reach these children as soon as possible to provide them with the aid they need."
Against this background, Saudi Arabia's ministry of culture and information announced on Saturday that Crown Prince Mohammed bin Salman has donated $66.7m to the WHO and UNICEF to fight cholera in Yemen.
Source: Al Jazeera and news agencies