A cholera outbreak in war-ravaged Yemen has killed 242 people, and left nearly 23,500 others sick in the past three weeks alone, the World Health Organization said Friday.

The UN health agency said that in the past day alone, 20 cholera deaths and 3,460 suspected cases had been registered in the country, where two-thirds of the population are on the brink of famine.

"The speed of the resurgence of this cholera epidemic is unprecedented," WHO country representative for Yemen Nevio Zagaria told reporters in Geneva by phone from Yemen, warning that a quarter of a million people could become sick by the end of the year.

Cholera is a highly contagious bacterial infection spread through contaminated food or water.

Reining in the disease is particularly complicated in Yemen, where two years of devastating war between the Huthis and government forces backed by a Saudi-led Arab military coalition has left more than half the country's medical facilities out of service.

Zagaria pointed out that humanitarian workers cannot access some parts of the country, and that the number of suspected cholera cases could be far higher than those registered.

Yemen's conflict has killed more than 8,000 people and wounded around 40,000 since March 2015, according to the WHO.

Zagaria pointed out that many of the remaining health workers in the country had not been paid for seven months.

At the same time, he said, lacking electricity meant water pumping stations were only functioning in an intermittent way, and the sewer systems were damaged.

"The population is using water sources that are contaminated," he said.

Zagaria said the United Nations agencies were preparing to "release an emergency response cholera plan in the next 48 hours," aimed at dramatically scaling up the number of treatment centres and rehydration centres.

At the same time, he said there was a dire need for funding to help Yemen authorities to make the necessary infrastructure repairs.

"The spread of the disease is too big and they need substantial support, in terms of repairing the sewer system, ... treating and chlorinating the water sources."

Without dramatic efforts to halt the spread of the disease, "the price that we will pay in terms of life will be extremely high," he warned.