"Now it is time for action," Somalia's special drought envoy Abdirahman Abdishakur Warsame said at an event in New York during the annual high-level meeting of the U.N. General Assembly. He urged world leaders to be generous.
U.N. Secretary-General Antonio Guterres warned that the people in the Horn of Africa were "staring into the abyss of humanitarian catastrophe."
"It is difficult to overstate the magnitude of the unfolding disaster, but if we act now, we can prevent the worst," he said in a recorded message.
The head of the U.S. Agency for International Development (USAID), Samantha Power, said Washington would provide another $151 million to address needs in Somalia.
"There are a lot of challenges facing the world, but almost none as acute as this one right now," Power said. "We still have a narrow window of opportunity to stave off famine in the Horn."
Italy, the United Kingdom and Qatar also pledged additional funds to respond to the crisis at Wednesday's event, but U.N. aid chief Martin Griffiths said more was needed.
The Horn of Africa is experiencing its worst drought in 40 years and experts say the region is on track for a fifth consecutive failed rainy season.
The United Nations has warned that parts of Somalia will be hit by famine in coming months. The projection is more severe than in 2011, when famine killed more than a quarter of a million Somalis, around half of whom were children.