The UN is warning that the world is facing the biggest humanitarian crisis since 1945.

Humanitarian chief, Stephen O'Brien estimates more than 20 million people in four countries are facing starvation and famine.

He has told the Security Council "without coordinated global efforts, people will simply starve to death" and "many more will suffer and die from disease".

Mr O'Brien says Yemen, South Sudan, Somalia and northeast Nigeria are in crisis: