Somalia, hit by drought and on the verge of famine, will count 1.4 million acutely malnourished children by the end of the year, up 50 percent from late 2016, the UN said Tuesday.
The United Nations children's agency warned that 275,000 of those children were expected to be so severely malnourished that they could easily die.
Severe acute malnutrition is the most extreme and visible form of undernutrition, with victims often appearing skeletal and frail, and in urgent need of treatment to survive.
Such children "are nine times more likely to die of cholera, or diarrhoea or measles," UNICEF spokeswoman Marixie Mercado told reporters in Geneva.
"The combination of malnutrition and disease, plus displacement is deadly for children," she said, pointing out that a severely malnourished and dehydrated child can die in a matter of hours from diarrhoea or cholera.
The World Health Organization warned last month that the drought was fuelling an outbreak of cholera and acute diarrhoea in Somalia that has already killed hundreds of people.
The warning comes as Somalia faces the threat of its third famine in 25 years of civil war and anarchy.
At least 260,000 people died in the 2011 famine in Somalia -- half of them children under the age of five, according to the UN World Food Programme.
Mercado pointed out that during that famine, "the major killer of children were diarrhoea and measles."
The dire drought and food situation has forced more than 615,000 people to flee their homes since last November, in a country where 1.1 million people are already internally displaced.
Unicef's representative in Somalia, Steven Lauwerier, cautioned in a statement that women and children on the move especially "are extremely vulnerable".
Women and children who move about in search of assistance "are often robbed or worse, both on the way to and in camps," the statement said.
The UN has appealed for $720 million to provide aid to Somalia this year, of which it so far has received $415 million, or about 58 percent, UN humanitarian agency spokesman Jens Laerke told reporters.