Arriving in their hundreds every day to seek relief in overcrowded Kenyan camps, weak and weary Somalis fleeing extreme drought and conflict face a new struggle to get food and shelter.

Like thousands of fellow Somalis, Adan Ahmed made the long and dangerous trek through the parched and famine-struck lands of southern Somalia, hiding from militia gunmen to escape into neighbouring Kenya.

"It is better here than in Somalia, but it is still not that good," said Ahmed, who is now struggling for his children's survival in the giant Dadaab refugee camp in eastern Kenya.

Conditions in refugee camps are grim, as the pressure grows each day with swelling numbers sharing limited supplies of food, medicine, shelter and water.

"There is hardly any food and lots of problems," he added sadly.

Around 1,300 Somalis flee each day into neighbouring Kenya in the desperate search of support.

"For me and my children, the future does not look good here," 60-year old Ahmed added.

Dadaab -- a tightly packed settlement of huts made of rags and plastic sheeting -- is the world's largest refugee complex.

The dust-blown series of camps in eastern Kenya are home to over 380,000 mainly Somalis fleeing drought and war.

"On our journey here we were attacked twice -- they took some of our clothes and our food," said 80-year-old Howa Hassan Abdi, waiting in a giant queue for measles and polio vaccinations for her four grandchildren.

"When we got here, my grandchildren got treatment as they were very sick and very hungry, but they got treated, and we got food," added Abdi, who fled from the region around Somali's dangerous capital two months ago.

"The only thing we are suffering is that there are no toilets."

The UN has declared a famine in two regions of southern Somalia controlled by Al-Qaeda affiliated rebels, but the effects have been felt more widely across the country, as well as in parts of Djibouti, Ethiopia, Kenya and Uganda.

The flood of refugees have stretched aid workers to the limits.

"Every day more than 1,300 people arrive here," said William Spindler, a spokesman for the UN refugee agency, UNHCR.

"The population is growing and there's no prospect of that stopping."

Despite growing international criticism, a purpose-built camp extension able to house some 40,000 more people -- complete with tin-roof houses and pit latrines -- remains closed.

Senior Kenyan government officials have made repeated assurances that the camp called Ifo II can open, but it also fears an infiltration by Somali Islamist Shebab insurgents.

With a formal decision still to be made, aid workers have been forced to move refugees into a separate extension of basic tents, where latrines are still being constructed.

"If the exodus from Somalia continues there will be no room for all of the refugees here in Dadaab," added Spindler worriedly.

Some in government have argued that feeding centres should be set up inside Somalia instead, but aid workers are restricted in the help they can offer there, given the risks of operating in a war-torn region where kidnap is common.

"We are present in Somalia, and we are already helping people," Spindler added.

"But we are not reaching all those who need our help, because of the insecurity, the presence of militia and because of the ongoing combat inside Somalia."

Some are succeeding -- the International Committee of the Red Cross said on Monday it had distributed food to 162,000 people in south and central Somalia, regions largely controlled by Islamist rebels.

But the challenges of supporting even those who have left the danger zones in Somalia remain enormous.

Malnutrition rates in Somalia are currently the highest in the world, weakening a population where few have received even basic immunisations.

In response, the UN children agency UNICEF launched on Monday a five-day mass vaccination campaign for polio and measles.

"Teams are going from tent to tent, to make sure all children aged between six months and five years are given life-saving vaccines," said Melissa Corkum, a UNICEF spokeswoman.

"There are cases of measles in the camp as children are coming from Somalia, where immunisation is very low."