Around 3.2 million children are expected to suffer from acute malnutrition in Afghanistan by the end of this year, with 1 million of them at risk of dying as temperatures drop, a World Health Organisation spokesperson says.
Aid agencies have warned of famine as a drought coincides with a failing economy following the withdrawal of Western financial support in the aftermath of a Taliban takeover in August.
The health sector has been hit especially hard, with many healthcare workers fleeing due to unpaid salaries.
"It's an uphill battle as starvation grips the country," Margaret Harris told Geneva-based journalists by telephone from the capital Kabul. "The world must not and cannot afford to turn its back on Afghanistan."
Nighttime temperatures are falling below zero degrees Celsius and colder temperatures are expected to make the old and the young more susceptible to other diseases, Harris said. In some places, people are chopping down trees to provide fuel for the hospitals amid widespread shortages, she added.
Harris did not have numbers for the number of children who had already died from malnutrition but described "wards filled with tiny little children", including with a seven-month old baby whom she described as "smaller than a newborn".
Measles cases are rising in the country and WHO data shows 24,000 clinical cases had so far been reported.
"For malnourished children, measles is a death sentence. We will see so many more deaths if we don't move on this quickly," Harris said.