A US$200m appeal is to be launched shortly
The United Nations has warned that Kenya, Yemen, South Sudan and Somalia are facing or are at risk of famine.
Its top humanitarian official Stephen O'Brien has urged the international community for comprehensive action to save people from "starving to death".
Mr O'Brien told the UN Security Council: "We stand at a critical point in history.
"Already at the beginning of the year we are facing the largest humanitarian crisis since the creation of the UN.
"The appeal for action by the Secretary-General can thus not be understated.
"It was right to sound the alarm early, not wait for the pictures of emaciated dying children...to mobilize a reaction and the funds", he added, calling for accelerated global efforts to support UN humanitarian action on the ground.
Without collective and coordinated global efforts, he warned, people risk starving to death and succumbing to disease, stunted children and lost futures.
Mr O'Brien has just returned from a visit to the affected nations.
He said that about two-thirds of the population (more than 18 million people) in Yemen needed assistance - including more than seven million severely food insecure.
While fighting continues to worsen the crisis.
"I continue to reiterate the same message to all: only a political solution will ultimately end human suffering and bring stability to the region".
In South Sudan, where a famine was recently declared, more than 7.5 million people are in need of assistance, including some 3.4 million displaced. The figure rose by 1.4 million since last year.
"The famine in the country is man-made. Parties to the conflict are parties to the famine - as are those not intervening to make the violence stop", he said, calling on the South Sudanese authorities to translate assurances of unconditional access into "action on the ground."
Similarly, more than half the population of Somalia (6.2 million people) is need aid, 2.9 million of whom require immediate assistance.
Extremely worrying is that more than one million children under the age of five are at the risk of acute malnourishment.
Mr O'Brien commented: "The current indicators mirror the tragic picture of 2011, when Somalia last suffered a famine" - but he expressed hope that a famine can be averted with strong national leadership and immediate and concerted support by the international community.
On Kenya, he mentioned that more than 2.7 million people were food insecure, and that this number could reach four million by April.
"In collaboration with the government [of Kenya], the UN will soon launch an appeal of US$200m (€187.3m) to provide timely life-saving assistance and protection".