The world faces the largest humanitarian crisis since the United Nations was founded in 1945 with more than 20 million people in four countries facing starvation and famine, the U.N. humanitarian chief said.

Stephen O’Brien told the U.N. Security Council that “without collective and coordinated global efforts, people will simply starve to death” and “many more will suffer and die from disease.”

He urged an immediate injection of funds for Yemen, South Sudan, Somalia and northeast Nigeria plus safe and unimpeded access for humanitarian aid “to avert a catastrophe.”

“To be precise,” O’Brien said, “we need $4.4 billion by July.”

Without a major infusion of money, he said, children will be stunted by severe malnutrition and won’t be able to go to school, gains in economic development will be reversed and “livelihoods, futures and hope will be lost.”