Almost six million people living in more than half of Niger's villages are facing a food and nutrition crisis, the UN warned on Friday.

"Approximately 6,900 villages out of 10,000 are in a vulnerable situation," said Elisabeth Byrs, spokeswoman for the UN Office for the Coordination of Humanitarian Affairs (OCHA).

Niger's government, assisted by the UN and humanitarian organisations, will assess next month the exact number of people who are most vulnerable, Byrs said.

Last month Niger's government said the drought-hit country had harvested 500,000 tonnes less cereal than required, raising concerns of a food shortage crisis right across the Sahel.

The OCHA said that already by June the rate of child malnutrition had reached alarming levels in seven out of eight regions.

In western Tillabery, one of the worst drought-affected areas, acute malnutrition was affecting more than 13 percent of inhabitants.

In 2009 Niger suffered a 400,000-tonne cereal shortfall, leading the following year to one of the worst food crises in its history.

"Even if the food situation in Niger improved slightly in 2011 ... the effects of the major food and nutrition crisis in 2010 reduced rural populations' capacity to survive," OCHA said.