The disease is now affecting 20 out of Yemen's 22 provinces, with more than 124,000 suspected cases, said the WHO on Monday.
The WHO predicted in May that the cholera outbreak could affect as many as 300,000 people within six months. A state of emergency was declared in Sana'a in May in response to the outbreak.
The international charity group Oxfam says the disease is killing one person an hour in Yemen.
Two years of war have put a huge strain on Yemen's healthcare system, and thousands of those infected with cholera are not able to access treatment.
Medicines and intravenous fluids are rapidly running out, and many health workers have not been paid for nearly nine months, according to UNICEF.
"My sister is sick and pregnant. She is about to die because there are no doctors or clinic. We can't even get any vaccinations," Eman Al-Bouraee told Al Jazeera.
More than 400 families who escaped fighting from different parts of the country and have taken shelter near a sewage treatment plant on the coast of Yemen’s Red Sea, now fear that the epidemic might hit them.
"Having people living in the sewage plant ground is a disaster. Women and children can easily fall victim to the disease. I want a charity or humanitarian organisations to take these people away from here," treatment plant engineer Ameen Kasem Heggy told Al Jazeera.
This is the second outbreak of cholera in less than a year in Yemen, the Arab world's poorest country in the grip of a war with no end in sight between government forces, which are backed by an Arab coalition, and Houthi fighters.
On the second anniversary of the war the UN said that an average of 100 people lose their lives monthly owing to the war, meaning that cholera is now killing people at a significantly faster rate.
An acute diarrhoeal infection, cholera is caused by the ingestion of food or water contaminated with the bacterium Vibrio cholera.
More than 10,000 people have been killed and millions displaced in more than two years of war, which has also destroyed much of the country's infrastructure.
Only a few medical facilities are still functioning and two-thirds of the population are without access to safe drinking water, the UN has said.
Source: Al Jazeera News