The crisis in Yemen that has left millions hungry and on the brink of famine is "a man-made disaster" driven not only by decades of poverty and lack of investment but also by economic strangulation being used as a tactic of war, the UN development chief in the country said Tuesday.

Auke Lootsma said "there is no end in sight" to Yemen's civil war and about 70 per cent of the country's 27 million people need humanitarian aid, 60 per cent don't know where their next meal is coming from, and nearly 7 million "are close to slipping into a state of famine."

In addition, he said, the UN has recorded almost 400,000 cases of cholera and nearly 1,900 related deaths in the past four months – and in the last two weeks there has been a meningitis outbreak.

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Lootsma told UN reporters by video conference from Yemen's capital, Sanaa, that nearly 2 million children are considered "acutely malnourished," which makes them susceptible to cholera – and cholera creates more malnutrition.

"We expect this cholera outbreak to continue to wreak havoc despite the best efforts of the UN agencies" and humanitarian agencies working on the ground, said Lootsma, who is the UN Development Program's country director in Yemen.

Yemen, which is on the southern edge of the Arabian Peninsula, has been engulfed in civil war since September 2014, when Houthi Shiite rebels swept into Sanaa and overthrew President Abed-Rabbo Mansour Hadi's internationally recognized government.

In March 2015, a Saudi-led coalition, backed by the United States, began a campaign against Houthi forces allied with ousted President Ali Abdullah Saleh in support of Hadi's government. Since then, the Iranian-backed Houthis have been dislodged from most of the south, but remain in control of Sanaa and much of the north.

Lootsma said 90 per cent of Yemen's food is imported "so imports are crucial," and at the moment getting food into the country is difficult because there are few commercial importers, they face financing challenges including getting credit, airports are closed to commercial flights and there are difficulties at ports.

"Foreign exchange reserves are depleted and the country is facing a liquidity crisis as well as a hard currency shortage," he added.

But Lootsma said the food crisis is mainly driven by the impact of increased food prices, and especially the reduction in purchasing power of Yemenis, many who were living in poverty before the conflict began.

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"So although food may be available in the market it is financially out of reach for many of the poor families at this point of time," Lootsma said.

Yemen is like "a bus racing towards the end of a cliff," he said. "Instead of hitting the brakes and turning around, the one that controls the bus keeps going and pushes the accelerator, all but certain to crash."

But, he added, "I think we can still stop this bus and turn it around before it goes over the cliff, but time is really running out, and it's really running out to find the brakes, and stop this from happening."

Lootsma said the most important need is stopping the war.

He said there is also a shortage of funds to help Yemenis. The UN humanitarian appeal for $2.1-billion is only 45 per cent funded and he urged donors who made pledges in April to send in the money.