DALLI, Niger (Reuters) - United Nations humanitarian agencies sounded the alarm on Tuesday about a growing food crisis in the West African state of Niger, but said it was too soon to talk of famine.

John Holmes, the U.N.'s top aid official, heard appeals for help from residents in Niger's arid east where many are on the move in search of food, but warned the U.N. had no miracle solution to the problem in one of the world's poorest countries.

Erratic rainfall last year devastated crops and livestock herds, leaving millions of people hungry in the uranium producer nation and the broader Sahel region.

In Diffa, more than 1,000 km (600 miles) southeast of Niger's capital, Niamey, many people have abandoned their homes in search of food, while others who remain are harvesting green fruits from usually inedible plants.

The teacher in Diffa said 15 children left the school last week alone. Skinny cattle and goats stood in the sun next to Chinese workers constructing a multi-billion dollar oil pipeline project in the region.

"We planted but the harvest was not good. Since then we have been waiting for manna, from wherever it can come," Maria Ali, a 55 year-old mother of 10, told Holmes in Diffa.

Holmes responded: "We do not have a miracle solution but we'll do our best." The U.N. is running a food-for-work programme for villagers who remain, paying them for clearing the main road threatened by the encroaching desert.

HUMANITARIAN CRISIS

Elisabeth Byrs, spokeswoman for the U.N. Office for the Coordination of Humanitarian Affairs (OCHA), said less than a third of the $190 million it is seeking from international donors to respond to the crisis has been raised.

While Byrs said it was too early to speak of famine, she told a briefing: "If we don't get this financing we could have an extremely serious humanitarian crisis in the country".

Aid agencies need to start work in earnest in June or July to stave off hunger problems, she added.

Niger risks a repeat of a severe hunger problem in 2005. At the time, Niger's President Mamadou Tandja tried to play down the problem until media attention made his stance untenable.

A government survey in December estimated 58 percent of the population, or 7.8 million people, were food-insecure.

The military rulers who ousted Tandja in a February coup have talked openly of the danger of famine in a move that aid agencies hope will improve efforts to tackle the crisis.

But acute malnutrition is increasing and more than 1.5 million children risk becoming malnourished over the next 12 months if urgent action is not taken, OCHA said.

The U.N. is trying to estimate numbers of people fleeing the countryside for urban areas or neighbouring countries.

The World Food Programme is also doubling the number of people who receive its food aid under its relief programme to 2.3 million. It said it normally needs 3-4 months to deliver food to Niger, and immediate contributions would enable it to procure food in the region, such as in Nigeria.

Niger's military rulers have taken tentative steps towards restoring civilian rule and meeting a donor-imposed deadline of polls by the end of the year, but the food crisis risks derailing the process.

In the United Nations' 2009 human development index, Niger ranks last out of 182 countries covered.