People in war-torn Yemen are facing a situation that "looks like the Apocalypse", the UN's humanitarian chief has told Al Jazeera, warning that the country could become the worst humanitarian disaster in half a century.

The Arab world's poorest country has endured nearly three years of war between Houthi rebels and Saudi-backed forces loyal to exiled President Abd-Rabbu Mansour Hadi.

The conflict is having a devastating effect, causing widespread food shortages and a major cholera outbreak as well as leaving millions in need of humanitarian assistance.

"The situation in Yemen - today, right now, to the population of the country - looks like the apocalypse," Mark Lowcock, the head of the UN office for the coordination of humanitarian Affairs (OCHA), said on Friday.

"The cholera outbreak is probably the worst the world has ever seen with a million suspected cases up to the end of 2017."

Lowcock said "a terrible new epidemic" of diphtheria, a bacterial disease which should be completely preventable by immunisation, has already "affected up to 500 people with dozens and dozens of deaths" in the past few weeks

"That is going to spread like wildfire," he added.

"Unless the situation changes, we're going to have the world's worst humanitarian disaster for 50 years".

'Desperate situation'

Lowcock's comments came as the UN's Central Emergency Response Fund (CERF) allocated $50m to bolster the relief effort in Yemen, where more than eight million people are on the brink of famine.

The sum represents the largest ever allocation made by CERF and reflects the dire situation in Yemen, which was already one of the Arab world's poorest countries before the start of the war in 2015.

Lowcock said the money would help prepare the necessary aid for the year ahead.

"The fact that I'm having to do that is obviously not a success measure, that is a sign of how desperate the situation is," he told Al Jazeera.

In a statement released on Friday, the UN said the money would "enable scale up of urgent life-saving assistance" in Yemen and would be directed towards famine prevention, as well as assisting civilians affected by the ongoing conflict.

Some of the money will also be used to support the country's deteriorating public services.

Missile 'intercepted'

Saudi Arabia and its allies intervened in neighbouring Yemen in March 2015 in an attempt to push back the Houthi, who are said to be backed by Iran, and restore Hadi's government.

Aid agencies have repeatedly said the Saudi-led coalition air raids and a debilitating blockade on the country's air and sea ports have depriving large areas of food, fuel and medicine.

The blockade, which was tightened last November, was eased three weeks later under massive international pressure.

Hospitals are also struggling to cope with demand amid the world's worst cholera epidemic on record and supply shortages caused by the blockade.

Several medical facilities have also reportedly been destroyed in air raids.

According to the UN, the conflict has killed more than 10,000 people and displaced three million.

Friday's aid announcement came as Saudi Arabia said it intercepted a missile fired by Houthi rebels at a military installation in Najran.

This is the latest in a series of missiles allegedly fired by the Houthis, to be intercepted by Saudi Arabia, including ones which targeted the Saudi capital, Riyadh.