Landlocked Niger, one of the poorest countries in the world, was devastated by an invasion of locusts that ate everything green last year, followed by a severe drought.
"We are having an acute humanitarian crisis in Niger in which children are dying as we speak," said UN relief coordinator Jan Egeland.
He added that Niger's severe food crisis could have been prevented if the United Nations had a reserve fund to jump-start humanitarian aid while appeals for money were considered.
"We need a central emergency fund so that we can have some predictability," Egeland said. "As of now we have none."
Charity group Oxfam said UN appeals for aid were "dangerously" under funded, with only one third of the money needed from donors being pledged. In many cases, the pledged money had not arrived, the agency added. the West African state
Niger was invaded by locusts in
2004 followed by a drought
The United Nations first appealed for assistance for Niger in November and got almost no response. Another appeal for $16 million in March got about $1 million.
The latest appeal on 25 May for $30 million has received about $10 million.
The UN "needs money now. Every day that the world's richest countries look the other way, more people face starvation. They have to put their hands in their pockets before it's too late", added Oxfam spokeswoman Natasha Kafoworola Quist.
On Wednesday, a first cargo plane packed with 18 tonnes of aid left France for the northeastern town of Maradi in Niger.
The Antonov plane was carrying
18 tonnes of aid for Niger
The airlift was to continue on Saturday and Sunday and were to make between eight and 10 trips between Ndjamena and Maradi over the weekend, taking 40 tonnes of grain and 28 tonnes of groundnut oil.
The operation is being financed by several big companies.
"The situation is desperate. Even the limited food that is available has soared in price, rendering it unaffordable for most families, and there is no hope of any harvest for at least three months," said Quist.
"Families are feeding their children grass and leaves from the trees to keep them alive."
But the West African state's situation is not unique - more than 18 million people are faced with serious food shortages in 10 African countries, a food security monitoring group said.
The US-funded Famine Early Warning Systems Network said in a report released late on Tuesday that more than 18 million people in 10 African countries faced food shortages because of poor rains and high crop prices.
"Families are feeding their children grass and leaves from the trees to keep them alive"
Natasha Kafoworola Quist,
It added that diminishing water supplies and dry pastures were fuelling conflict among rival tribes, and child malnutrition was reportedly rising in parts of the Greater Horn of Africa region.
The food shortages were concentrated in Ethiopia, where more than half of the 18 million affected people live, the report said. At least half of neighbouring Eritrea's population of 4.5 million was in peril, as well as 2.69 million in Uganda.
Other countries affected include Sudan, Djibouti, Rwanda, Tanzania, Kenya, Burundi and Somalia, it said.