About 65,000 people are affected according to the latest food security assessment. Staff from an aid agency had counted the graves of 430 children who had died of hunger over the past few weeks in Nigeria.
Tens of thousands of people are going hungry in the west African region where Boko Haram militants are active, the UN humanitarian coordinator for the region said at a news conference on Friday.
About 65,000 people are in a "catastrophe" or "phase 5" situation according to a food security assessment by the IPC, the recognised classification system used to declare famines.
Phase 5 of the IPC applies where even with humanitarian assistance, "starvation, death and destitution" are due to occur.
"I can tell you from my first trip outside (the regional capital) Maiduguri, I had never gone to places that had adults who were so depleted of energy that they could barely walk," Toby Lanzer, the UN regional humanitarian coordinator said.
According to Lanzer, one aid agency reported from the Nigerian town of Bama that its staff had counted the graves of 430 children who had died of hunger in the past few weeks.
Boko Haram militants have killed about 15,000 people and displaced more than 2 million in a seven-year insurgency and they still launch deadly attacks despite having been pushed out of the vast swathes of territory they controlled in 2014.
"Because of the insecurity sown almost exclusively by Boko Haram, people have missed three planting seasons," Lanzer added.
Millions more are short of food in northern Nigeria and regions in the adjoining countries, signalling that the situation could get worse and so turn into the "biggest crisis facing any of us anywhere," Lanzer said.
"We're now talking about 568,000 across the Lake Chad basin who are severely malnourished, 400,000 of them are in the northeast of Nigeria. We know that over the next 12 months, 75,000, maybe as many as 80,000, children will die in the northeast of Nigeria, unless we can reach them with specialised therapeutic food."