Nearly one million children across eastern and southern Africa are suffering from "severe acute malnutrition" after two years of drought and the strongest El Nino in 50 years, UNICEF said Wednesday.
Children in the region face worsening food and water shortages, with rising prices exacerbating the situation as families are forced to skip meals and sell belongings.
"Severe acute malnutrition" is defined as extreme hunger, causing a very low weight-for-height ratio, visible wasting or fluid retention.
"The El Nino weather phenomenon will wane, but the cost to children -- many who were already living hand-to-mouth -- will be felt for years to come," said UNICEF regional director Leila Gharagozloo-Pakkala.
"Governments are responding with available resources, but this is an unprecedented situation. Children's survival is dependent on action taken today."
The agency is running humanitarian appeals calling for $87 million for Ethiopia, $26 million for Angola and $15 million for Somalia.
Lesotho, Zimbabwe, and most of South Africa have declared drought emergencies, while in Ethiopia, the number of people in need of food assistance is expected to increase from 10 million to 18 million this year.
Malawi is facing its worst food crisis in nine years, with 2.8 million people (more than 15 percent of the population) at risk of hunger and "severe acute malnutrition" doubling in only two months.
"The statistics are staggering," said Megan Gilgan, UNICEF regional emergency advisor. "The situation is expected to worsen throughout this year and into 2017."
Last month the UN's World Food Programme (WFP) said 14 million people across southern Africa faced going hungry after a prolonged drought wrecked harvests.
The WFP said the cost of maize, also called corn, in Malawi was 73 percent higher than average.
South Africa will import half its average maize crop after 2015 was declared the driest year in more than a century.
In Ethiopia, 435,000 children were said to be in need of treatment for severe acute malnutrition.
"We are dealing with a slow onset crisis affecting countries in different ways," Gilgan said. "The outlook is disturbing, with little or no rain falling in affected areas."
UNICEF said conditions were worse than the 2011 Horn of Africa food crisis that hit Somalia, Ethiopia, Djibouti, Kenya and Uganda.
Apart from hunger, the spread of diarrhoea, cholera and typhoid has also been reported.
Sparked by warming in sea surface temperatures in the equatorial Pacific, El Nino periodically wreaks havoc on world weather patterns, causing drought in some parts and floods in others.