Updated March 11, 2017 17:41:57

Photo: The magnitude of the violence in war-torn Yemen has not been widely publicised. (Supplied: Taha Yaseen, file)

The world is facing the largest humanitarian crisis since 1945, with more than 20 million people in four countries facing starvation and famine, the United Nations humanitarian chief says.

Stephen O'Brien told the UN Security Council on Friday 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", describing the current situation as a "critical point" in history.

"To be precise," Mr O'Brien said, "we need $US4.4 billion by July".

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

UN and food organisations define famine as when more than 30 percent of children younger than five suffer from acute malnutrition, and when mortality rates are two or more deaths per 10,000 people every day, among other criteria.

"Already at the beginning of the year, we are facing the largest humanitarian crisis since the creation of the United Nations," Mr O'Brien said.

"Now, more than 20 million people across four countries face starvation and famine."

Photo: More than 1 million children are estimated to be acutely malnourished in South Sudan. (Supplied: UNICEF, file)

Mr O'Brien said the largest humanitarian crisis is in Yemen where two-thirds of the population — some 18.8 million people — need urgent food aid.

"That is 3 million people more than in January," he said.

The Arab world's poorest nation is engulfed in conflict and Mr O'Brien said more than 48,000 people fled fighting just in the past two months.

During his recent visit to Yemen, Mr O'Brien said he met senior leaders of the Government and the Shiite Houthi rebels who control the capital Sanaa, and all promised access for aid.

Charities are calling for an urgent increase in aid spending to avoid a "catastrophe" across the Middle East and North Africa.

"Yet all parties to the conflict are arbitrarily denying sustained humanitarian access and politicise aid," he said.

Mr O'Brien warned that if behaviour doesn't change now, those parties "must be held accountable for the inevitable famine, unnecessary deaths and associated amplification in suffering that will follow."

Catastrophes across Africa

The UN humanitarian chief also visited South Sudan, the world's newest nation which has been ravaged by a three-year civil war, and said "the situation is worse than it has ever been".

"The famine in South Sudan is man-made," he said.

"Parties to the conflict are parties to the famine as are those not intervening to make the violence stop."

Mr O'Brien said more than 7.5 million people need aid, up by 1.4 million from last year, and about 3.4 million South Sudanese were displaced by fighting including almost 200,000 who have fled the country since January.

Photo: While Boko Haram have dropped out of the headlines their uprising has continued. (Reuters/ Afolabi Sotunde, file)

"More than 1 million children are estimated to be acutely malnourished across the country, including 270,000 children who face the imminent risk of death should they not be reached in time with assistance," he said.

"Meanwhile, the cholera outbreak that began in June 2016 has spread to more locations."

In Somalia, which Mr O'Brien also visited, more than half the population of 6.2 million people need humanitarian assistance and protection, including 2.9 million who are at risk of famine and require immediate help "to save or sustain their lives".

He warned that close to 1 million children under the age of five will be "acutely malnourished" this year.

In north-east Nigeria, a seven-year uprising by the Islamic extremist group Boko Haram has killed more than 20,000 people and driven 2.6 million from their homes.

A UN humanitarian coordinator said last month that malnutrition in the north-east is so pronounced that some adults are too weak to walk and some communities have lost all their toddlers.

Photo: Thousands have been streaming into Somalia's capital Mogadishu in search of food aid. (AP: Farah Abdi Warsameh, file)

AP

Topics: famine, relief-and-aid-organisations, unrest-conflict-and-war, world-politics, yemen, nigeria, south-sudan, somalia

First posted March 11, 2017 16:41:35