UNICEF says malnutrition and food shortages, largely the result of chronic under-development and a worsening water crisis, is acute.
"It's an emergency very much comparable to the Horn of Africa and the Sahel in North Africa, but it's not getting as much attention," said Geert Cappelaere, the UNICEF chief in Yemen.
He urged donors to make the fight against malnutrition the top priority in the development agenda for Yemen, where for years economic projects have been overwhelmed by the fight against al-Qaida and more recently the political turmoil triggered by the Arab Spring of 2011.
Both crises were sharpened by the February fall from power of President Ali Abdullah Saleh, who ruled for 33 years, and a major escalation of the U.S.-backed war to crush al-Qaida.
With the army divided between supporters of Saleh and his family, who still hold senior posts, and Saleh's successor as president, his longtime deputy Gen. Abdu Rabbo Mansour Hadi, Cappelaere said the food crisis is worsening.
With 58 percent of children under the age of 5 stunted by malnutrition, Yemen has the second highest rate of chronic malnutrition in the world, behind Afghanistan, he noted.
Acute malnutrition has hit up to 30 percent of children in those areas hit most by the fighting, he said.
That's close to levels in nearby southern Somalia, another battleground between Western-backed forces and Islamist militants of al-Shabaab, which is also aligned with al-Qaida.
Cappelaere called on the international community to focus its resources as much on Yemen's development as it does on the security emergency because unless development moves forward the security battle will be lost.
The lack of access to water is a key factor in the growing food crisis, he said.
"Close to 60 percent of Yemenis have difficulty in getting drinking water," he said.
"Last year's conflict was about politics but what will be the next source of conflict? It may well be the struggle for water."
Yemen's oil reserves, pegged at 4 billion barrels in the 1990s, a meager total by Middle East standards, are dwindling rapidly. That's critical because oil is responsible for 75 percent of state revenues and 90 percent of exports.
With Yemen expected to become a net oil importer by 2016, the country needs to diversify its economy fast -- an unlikely prospect right now.
What's worse is the country's water is running out.
At current rates, Sanaa, Yemen's ancient capital with a population of 2 million, looks like being dry by 2025, the first metropolis in the world to run out of water.
By all accounts, Yemen is facing economic collapse, a crisis that's probably more dangerous that al-Qaida's growing power or the escalating secret war against the jihadists being waged by U.S. President Barack Obama and could act in al-Qaida's favor.
"Unless urgent humanitarian action is taken, Yemen will be plunged into a hunger crisis of catastrophic proportions," Jerry Farrell, Save the Children's country director for Yemen, observed in May.
Much of the problem can be laid at the door of Saleh, whose long rule was notorious for its culture of corruption and inept governance. He failed to build infrastructure that would have averted the looming calamity and it was possibly for this as much as his repression of Yemen's 23 million people that the country now faces a humanitarian crisis.
Growing water scarcity, with highland aquifers shrinking 10-20 feet a year, is threatening agriculture in Yemen whose population, the World Bank says, is exploding at an estimated 8 percent a year.
The water problem, hidden by the security crises, was worsened because Yemenis use 40 percent of their available water to grow qat, a mildly narcotic plant that's the country's largest cash crop and highly prized across the Arabian Peninsula. That's far more than they allocate to grow food.
The World Food Program says one-fifth of the population, around 5 million people, is in need of emergency food aid.
The United Nations warned that 500,000 children may die in 2012 from malnutrition or famine, with around 750,000 children under 5 malnourished.