After two years of civil war, the World Food Programme says the country is on the brink of famine.
The sheer scale of the deprivation is staggering: of Yemen's 25.6 million people, almost 19 million are in urgent need of assistance, the UN says.
Almost seven million are "severely food insecure", meaning they need food aid immediately. Two million children are acutely malnourished.
"The situation is nothing short of catastrophic," says Robert Mardini, who is director of Middle East operations for the International Committee of the Red Cross (ICRC) and has recently returned from Yemen.
Despite repeated warnings about a potential disaster in Yemen, the UN's appeal for $2.1bn to bring relief is only 15% funded.
The key port of Hudaydah, which aid agencies describe as "a lifeline" for Yemen, is now virtually closed, due to a partial blockade by coalition forces, and the destruction of cranes in air strikes. This means that about only 30% of the supplies Yemen needs are getting into the country at all.
Unicef has calculated that a child is dying every 10 minutes from a preventable illness.
"A malnourished child is nine times more likely to die from a preventable illness than one which is properly nourished," explains Christophe Boulierac of the UN children's agency Unicef. "We have got to raise awareness of the terrible impact this conflict is having."