A cholera outbreak in war-ravaged Yemen has killed 315 people since April 27, the UN World Health Organization (WHO) said on Sunday.

The cholera infection is continuing to spread across Yemen with more than 29,300 suspected cases reported in 19 of the country's 22 provinces, the agency added in a tweet.

The latest tallies come a day after the international charity organisation Doctors without Borders warned that the cholera outbreak could get out of control in Yemen.

The impoverished country has been devastated by a power struggle between a Saudi-backed government and Iran-aligned rebels since late 2014. Yemen's ongoing violence has taken a toll on its healthcare centres.

Last week, a state of emergency was declared in the rebel-held capital Sana'a after a large number of cholera cases were detected in the city.

More than half of the country's medical facilities no longer function, the WHO said. Some 7.6 million people live in Yemen's cholera-threatened areas, according to UN estimates.

Potential 300,000 cases in six months

On Friday, the WHO warned that Yemen could have as many as 300,000 cases of cholera within six months and an "extremely high" number of deaths.

"We need to expect something that could go up to 200,000-250,000 cases over the next six months, in addition to the 50,000 cases that have already occurred," Nevio Zagaria, WHO Yemen representative, told reporters in Geneva.

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The cost in lives from an infection rate on this scale would be "extremely, extremely high", he said, adding that "the speed of the resurgence of the cholera epidemic is unprecedented [for Yemen]".

What is cholera?

Cholera, an acute diarrhoeal infection, is caused by ingestion of food or water contaminated with the bacterium Vibrio cholera.

If not treated, the disease can kill within a few hours. Almost 75 percent of people infected do not show any symptoms.

The short incubation period means outbreaks can spread with explosive speed, especially in places without safe water and proper sanitation, according to the WHO.

The US Center for Disease Control and Prevention (CDC) estimates three to five million cholera cases annually and over 100,000 deaths occurring each year.

Cholera can be simply and successfully treated by immediate replacement of the fluid and salts lost through diarrhea. Patients can be treated with oral rehydration solution, a prepackaged mixture of sugar and salts to be mixed with water and drunk in large amounts, according to the CDC.

Yemenis have been suffering from a significant lack of access to food, clean water, as well as medications that have contributed to the spread of the infection.