NAIROBI, Kenya — The world’s largest humanitarian crisis in 70 years has been declared in three African countries on the brink of famine, just as President Trump’s proposed foreign aid cuts threaten to pull the United States from its historic role as the world’s top emergency donor.

If the deep cuts are approved by Congress and the U.S. does not contribute to Africa’s current crisis, experts warn that the continent’s growing drought and famine could have far-ranging effects, including a new wave of migrants heading to Europe and more support for Islamic extremist groups.

The conflict-fueled hunger crises in Nigeria, Somalia and South Sudan have culminated in a trio of potential famines hitting almost simultaneously. Nearly 16 million people in the three countries are at risk of dying within months.

Famine already has been declared in two counties of South Sudan and 1 million people there are on the brink of dying from a lack of food, U.N. officials have said. Somalia has declared a state of emergency over drought and 2.9 million of its people face a food crisis that could become a famine, the U.N. said. And in northeastern Nigeria, severe malnutrition is widespread in areas affected by violence from Boko Haram extremists.

“We are facing the largest humanitarian crisis since the creation of the United Nations,” Stephen O’Brien, the U.N. humanitarian chief, told the U.N. Security Council after a visit this month to Somalia and South Sudan.

At least $4.4 billion is needed by the end of March to avert a hunger “catastrophe” in Nigeria, Somalia, South Sudan and Yemen, U.N. Secretary-General Antonio Guterres said in late February.

But according to U.N. data, only 10 percent of the necessary funds have been received so far.

Trump’s proposed budget would “absolutely” cut programs that help some of the most vulnerable people on Earth, Mick Mulvaney, the president’s budget director, told reporters last week. The budget would “spend less money on people overseas and more money on people back home,” he said.

The United States traditionally has been the largest donor to the U.N. and gives more foreign aid to Africa than any other continent. In 2016 it gave more than $2 billion to the U.N.’s World Food Program, or almost a quarter of its total budget. That is expected to be reduced under Trump’s proposed budget, former and current U.S. government officials said.

“I’ve never seen this kind of threat to what otherwise has been a bipartisan consensus that food aid and humanitarian assistance programs are morally essential and critical to our security,” Steven Feldstein, a former deputy assistant secretary of state in the Obama administration, told The Associated Press.

If Trump’s foreign aid cuts are approved, the humanitarian funding burden for the crises would shift to other large donors like Britain. But the U.S.’s influential role in rallying global support will slip.