UNITED NATIONS (Reuters) - More than $4 billion is needed by the end of March to help nearly 20 million people who risk starvation in Nigeria, Somalia, South Sudan and Yemen, United Nations Secretary General Antonio Guterres said on Wednesday.

Citing armed conflicts and climate change as part of the reasons for the food emergency, Guterres led a call for $5.6 billion in funding for humanitarian operations in the four countries this year, of which $4.4 billion are needed by the end of next month “to avert a catastrophe.”

“Despite some generous pledges, just $90 million has actually been received so far,” said Guterres, about two cents for every dollar needed.

“We are in the beginning of the year but these numbers are very worrying.”

Armed conflicts are having devastating humanitarian consequences, said Guterres, calling climate change a “key enhancer” of the humanitarian problem.

Last week, the U.N. World Food Programme’s chief economist told Reuters more than 20 million people in the four countries were at risk of dying from starvation within six months.

U.N. chief Guterres said Wednesday women and girls are disproportionately affected by the crisis and nearly half a million children are suffering severe acute malnutrition.

“Famine is already a reality in parts of South Sudan,” Guterres said. “Unless we act now, it is only a matter of time until it affects other areas and other countries. We are facing a tragedy.”

Yemen, where more than 10,000 people have died as part of a two-year-long conflict, is facing the largest food insecurity emergency in the world, Guterres said, with an estimated 7.3 million people needing immediate help.

Earlier on Wednesday, a senior U.N official said more than seven million people face starvation in Nigeria’s insurgency-hit northeastern region and around Lake Chad.