The UN World Food Programme is set to start airlifting food to Somalia, Ethiopia and Kenya after an emergency meeting in Rome on the drought-stricken Horn of Africa region.

An estimated 3.7million people in Somalia - about a third of the population - are on the brink of starvation and millions more in Djibouti, Ethiopia, Kenya and Uganda have been struck by the worst drought in the region in 60 years.

WFP chief Josette Sheeran said her organisation would begin food airlifts to the Somali capital Mogadishu, as well as aid flights to Dolo in Ethiopia on the border with Somalia and to Wajir in northern Kenya, which has been badly hit by drought.

The plight of children in Somalia is "the worst I have ever seen", she said, after visiting Mogadishu and the Dadaab refugee camp in Kenya at the weekend.

"Children are arriving so weak that many of them are in stage four malnutrition and have little chance - less than 40% chance - of making it," Sheeran said.

"The catastrophic situation demands massive and urgent international aid," Jacques Diouf, head of the UN Food and Agriculture Organisation, told participants at Monday's Rome meeting.

"It is imperative to stop the famine," declared by the UN this month in two insurgent-held areas of southern Somalia, Diouf said.

Officials said at Monday's meeting the UN has received about $1-billion since first launching an appeal for the region in November 2010 but needs a billion more by the end of the year to cope with the emergency.

The World Bank on Monday pledged more than $500-million, with the bulk of the money for long-term projects to aid livestock farmers and $12-million for immediate assistance to those worst hit by the crisis.

But charities voiced disappointment at the international response.

"It is shameful that only a few of the richest and powerful economies were willing to demonstrate today their commitment to saving the lives of many of the poorest and most vulnerable," said Barbara Stocking, the head of Oxfam.

UN officials say the drought has killed tens of thousands of people in recent months, forcing hundreds of thousands of desperate survivors from the worst-affected areas of Somalia to walk for weeks in search of food and water.