Less than 30 percent of pledged international aid has been delivered to Yemen this year, a U.N. official said Wednesday, as millions across the country struggle to survive.

Donors in April pledged close to $1.1 billion (981,500 euros) in aid to war-torn Yemen, which the U.N. Office for the Coordination of Humanitarian Affairs calls the "largest humanitarian crisis in the world".

But "only 25 percent of aid pledged to the UN refugee agency and 29 percent of aid pledged to the U.N.'s humanitarian response plan have been delivered so far," UNHCR's Yemen spokesperson Shabia Mantoo told AFP.

Some 19 million people are in need of aid in Yemen, with 10.3 million requiring immediate assistance to "save or sustain their lives", according to the U.N.

Yemen's deadly war has seen more than 8,000 people killed and millions displaced since a Saudi-led Arab coalition intervened to support a government fight against Shiite Huthi rebels allied with Iran.

Looming famine and an outbreak of cholera in Yemen, the most impoverished country long before the war, are taking their toll on the population.

"Conditions are only worsening. The cholera rates are alarming, health facilities are struggling to remain functional, millions across the country are food insecure and facing prolonged displacement from their homes," Mantoo said.

The International Committee of the Red Cross on Wednesday said 5,000 new suspected cases of cholera have been reported every day in Yemen, where an outbreak of the waterborne disease has killed more than 900 people since April 27.

A quarter of a million people are expected to contract cholera within six months, according to the World Health Organization (WHO).