The UN’s refugee agency said that of the more than 250,000 people forced from their homes since May, about 80 per cent are women or children.
“This is a staggering statistic,” the UNHCR's Shabia Mantoo said. “We need to raise the alarm about the disproportionate toll they are paying for what is happening on the ground.”
Many have fled to the capital Kabul or other cities but are sleeping in the open.
Save the Children estimated that 72,000 children have arrived in Kabul in the past few days.
“We fear the worst is yet to come and the larger tide of hunger is fast approaching … the situation has all the hallmarks of a humanitarian catastrophe,” the World Food Programme's Thomson Phiri said.
Jens Laerke, spokesman for the UN Office for the Co-ordination of Humanitarian Affairs, said the displaced were "sleeping in the open, in parks and public spaces”.
“Normally they would go to family and friends for shelter but this is no longer the case," he said.
Save the Children said many of the young people in Kabul were living on the streets in tarpaulin tents and were short of food.
A survey the charity carried out of those arriving in Kabul showed more than half reported having little to no food.
“This is a humanitarian disaster unfolding in front of the world’s eyes,” said Christopher Nyamandi, the country director for Save the Children in Afghanistan.
“Families already living in Kabul have brought the food they could spare to help the displaced but there’s just not enough. And more families are arriving every hour. We will start to see children going hungry or even sliding into malnutrition very soon.
“People are drinking water from dirty containers, the circumstances are unhygienic. We’re one step away from a disease outbreak.”
Many families were selling their possessions to be able to afford food, Save the Children said.
“The people of Afghanistan not only need the world’s attention, they need the world’s help to get through this. These are families with children, old people. Our staff came across at least 13 pregnant women. We can’t turn our back on them. We need tents, food, clean water, sanitation. Immediately.”
While countries are sending additional troops into Afghanistan to help their citizen leave, the UN said its 320 staff members would remain for now.