"In Nigeria, the government health infrastructure has completely collapsed in rural areas," said Ben Foot, Nigeria programme manager for Save the Children. "Even when there are drugs and equipment available people have to pay and they can't afford them."
At least 20 percent of children being treated in some of Save the Children's feeding centres in southern Niger's Maradi Region, across the border from northern Nigeria, are Nigerian. Other aid agencies in Niger said that close to the Niger-Nigeria border up to 90 percent of children being given nutritional supplements, vaccinations and free healthcare come from Nigeria.
Northern Nigeria and neighbouring Niger share the same semi-arid climate and reliance on rain-fed subsistence agriculture.
Nationally in Nigeria 29 percent of children are considered underweight, according to statistics drawn up by the UN children's agency (UNICEF). Many other key indicators which contribute to malnutrition are worse in Nigeria than Niger as well as many other countries in the Sahel (see fact box).
The north of Nigeria reportedly has at least twice the level of malnutrition and child mortality than Nigeria's south.
But across the border in Niger, a flood of donor funds for nutrition projects has led to a rapid improvement in children's health following major publicity for a nutritional crisis in 2005.
In some parts of Maradi Region, Niger, death rates among children under five have been reduced to the same levels as in the US because of micronutrient supplements, the education of women on breast feeding, improved access to clean water and large numbers of donor-funded NGOs.
Nigeria's chief nutritionalist at the ministry of health in Kano State, Saratu Abdullah, claimed there was absolutely no malnutrition in Nigeria. "We don't have malnourished children in this country," she said.
The government has not conducted a reliable nutritional survey since 2003. Save the Children's Foot said that the few other surveys that have been done in the region are "unreliable and pushing someone's agenda".
"The situation is clearly appalling but there's no hard data yet," Foot said.
Aid agencies have recorded Nigerians needing nutritional assistance in Niger since at least 2005, when Medecins sans Frontiers briefly set up a feeding centre in northern Nigeria's Katsina state to try to curb the flow of malnourished Nigerian children into Niger and to respond to a high level of malnutrition in Nigeria that year resulting from a measles epidemic.
But since then there have been few international NGO operating in northern Nigeria.
"Because of its oil riches people think Nigeria should be able to look after itself. But the government has been ripping the country off for the last 20 years, stripping resources and only taking care of its elite," Foot, from Save the Children, said.
Aid agency officials in Niger have said privately that they are concerned about making the issue of Nigerians coming to Niger public as it could prompt the Nigerian government to close the border or the authorities in Niger to scale down nutrition-related projects.
For Foot it is nonetheless better to acknowledge that there are problems in Nigeria. "The drift of malnourished Nigerians into Niger could be an indication of how many more Nigerians are barely surviving," he said.