More than 100,000 people have fled to Mogadishu from other drought-struck Somalia regions in search of food and water, but insecurity in one of the world's most dangerous cities is hampering aid flows.

"We are scaling up efforts in Mogadishu. The (UN refugee agency) UNHCR has brought in three planes of supplies including plastic sheeting and non-food items," Amos told AFP after a visit to Mogadishu.

UN relief agencies recently began airlifting emergency supplies to Somalia and the capital, where the displaced have been declared by the United Nations as facing famine.

"We felt we would not see famine again, but there it is. Children don't need to die needlessly. We absolutely need to work on long-term strategies," said Amos, the UN under-secretary general for humanitarian affairs and emergency relief coordinator.

Some 12 million people in parts of Ethiopia, Djibouti, Kenya, Uganda and Somalia are in danger of starvation in the wake of the region's worst drought in decades.

War-wracked Somalia is the country hardest hit by the Horn of Africa's drought, with five areas declared to be experiencing famine.

Much of the territory struck by famine is under the control of the Islamist Shebab militia, who have been blamed for exacerbating the humanitarian crisis by restricting aid to their regions.

Last weekend, the Al-Qaeda-inspired rebels made a surprise withdrawal from Mogadishu. Aid groups are now assessing how to expand relief distribution as the African Union forces protecting the Somali government try to secure the city.

"People were saying to me things have felt a little easier over the past few days. They are still worried about suicide attacks but want to seize any opportunity they can," Amos said.

"I was distressed in the hospital by the children," said Amos. "The mothers are devastated. To see children who are three or four years old look like babies brings home the challenge we are facing."

Somalia currently faces the most severe humanitarian crisis in the world and the worst food security crisis in Africa since its 1991-92 famine, according to the UN.

Political fallout from the toppling of then president Siad Barre from power spiralled Somalia into the bloody conflict that has engulfed it ever since and led to a famine which killed at least 300,000, according to UN estimates.

The United Nations estimates that $2.4 billion (1.7 billion euros) is required to address the current crisis.

Over 100,000 people have fled into Somalia's famine-hit and war-torn capital in the past two months in search of food, water and medicine.

But with makeshift camps already overcrowded, hundreds have sought refuge in the crumbling shell of the cathedral, built by Italian colonial authorities in the 1920s but destroyed in years of bloody civil war.

"We had to leave our land, because all the animals died," said Numur Moalim, who fled the drought-hit Bay region of southern Somalia, taking 15 days to trek into the dangerous capital with his wife and five children.

Huts are built on almost every space inside the cathedral, squeezed between giant chunks of masonry blasted from the still dramatic white stone building, while more huts are packed tight in the overgrown graveyard outside.

"I didn't come because it was a church, but because I needed protection and shelter, and there was nowhere else to go," Moalim said.

Sharp cracks of rifle fire ring out close by, with the sounds echoing in the high walls of the building, but Moalim does not flinch.

Shootings are common here, and heavily armed gunmen perched on top of pick-up trucks cruise the sandy streets nearby.

Instead, crouching on the rubble-strewn stone flags of the cathedral's floor, Moalim tries to chip out holes to slot in thin branches for the poles of the hut.

"We have nothing, and my children cry because they are hungry, but I have not got food to give them," he added, lifting up some of the plastic bags and small scraps of grubby material that will form the hut's patchwork roof.

High up on the wall above his head a life-size stone statues of Jesus Christ and his disciples -- their heads blasted with bullet holes -- stare down on the crowded people struggling for survival below.

Islamic extremists -- who still control much of southern and central Somalia and continue with a draconian ban on several foreign agencies -- reportedly used the cathedral for target practice.

Conflict-wracked Somalia is the country hardest hit by the extreme drought affecting 12 million people across the Horn of Africa.

The United Nations has officially declared famine in Somalia for the first time this century, including in Mogadishu and four southern regions.

Despite a withdrawal earlier this month from the city by the Al-Qaeda-affiliated Shebab rebels, government forces backed by African Union troops continue to struggle to secure one of the world's most dangerous capitals.

"People died in my village -- it was not a choice that we come here," said Huwa Adan Ismail, from the famine-struck Lower Shabelle region.

"It has rained heavily in the last few nights, and there is no protection from the rain -- it is so cold," she added.

Some of her seven young children peer out from holes in their rag hut, while Ismail struggles to boil a saucepan of grain over an open fire beneath a pillar of the cathedral.

"We are not getting enough support," said Mohamed Ahmed Ali, a community leader of the cathedral camp.

"People come and take assessments, and we see the aeroplanes coming in over our head to land, but we don't get the food that they bring," he added.