The United Nations says nearly 17 million people in the Horn of Africa are in urgent need of food and other aid - almost twice as many as earlier this year.
The UN says $US700 million in emergency aid is needed to prevent the region descending into full-scale famine.
Top UN humanitarian official John Holmes said food stocks are critically low in parts of Ethiopia, Somalia, Eritrea, northern Kenya and Uganda.
The area has suffered from drought, conflict and rocketing food prices.
The number of those at risk could rise still further "as the drought deepens and the hunger season continues", Mr Holmes says.
"What we need essentially is more funds, and more funds now, otherwise the situation is going to become even more catastrophic than it is today."
The estimated total for the rest of this year for those in need is $US1.4bn. Almost half of that has been raised, Mr Holmes said, but there remains a shortfall of $US716m.
"We may need significant funds after that period - this is not the end of the story," he said.
The UN Food and Agriculture Organisation blames worldwide rises in food prices for helping to push 75 million more people into the ranks of the world's hungry last year - bringing the total to 925 million.