UNICEF called on charities and donors to respond quickly to avert a tragedy in Borno state, where nearly a quarter of a million children are severely malnourished.
Most of the children are in areas that had been inaccessible before a multinational force liberated them from Boko Haram extremists earlier this year.
"Some 134 children on average will die every day from causes linked to acute malnutrition if the response is not scaled up quickly," the agency's regional director, Manuel Fontaine said.
The seven-year Boko Haram insurgency, which pledged support for the Islamic State group last year, has killed more than 20,000 people and spread across Nigeria's borders, forcing about 2.7 million people from their homes.
UNICEF said the agency has received less than half of the USD 55.5 million it appealed for earlier this year, and now the needs are even greater.