The World Food Program is flying 10 tons of food into Mogadishu and will apparently try and distribute the aid despite warnings from Islamists in control of much of the country.
The delivery was to have begun on Tuesday but was delayed from leaving Kenya by bureaucratic hurdles.
Islamist militias control most of Somalia and have banned the WFP from their areas.
The WFP delivery is the first airlift of food aid since the UN declared a famine in two southern areas of Somalia last week.
Thousands of people have fled to Mogadishu in search of assistance. The weak interim government, backed by an African Union force, controls only parts of the city.
Somalia is thought to be worst-hit by the crisis, but Ethiopia, Kenya and Djibouti have also been affected.
More than 10 million people in the region are thought to be at risk.
Somali Foreign Minister Mohamed Ibrahim has warned that more than 3.5 million people "may starve to death" in his country.
The Islamists say there is no famine in areas they control, but they also claim that the food aid would undercut local farmers trying to sell their harvests. The first claim is nonsense, but they may have a point with the second complaint. In fact, it is a common complaint made by local farmers whenever massive food supplies are shipped in to feed people in refugee camps and areas hit by drought. It's one of the major impediments to developing reliable local food supplies. It's been suggested that the UN buy food from local farmers to spur economic development, and this has been done in some areas. But Somalia is so destitute and without an economic base that it would do little good.