Hundreds of thousands of people continue to flee drought in East Africa, walking for days in search of food and water, with aid agencies saying the situation is now extremely serious.

Many of those fleeing have come to the Dadaab refugee complex, in northeastern Kenya, near the borders of Ethiopia and Somalia.

According to doctors in the area, most of the children have severe cases of acute malnutrition and related complications such as anaemia.

"The children are presenting with skin complications where their skin is peeling off mainly due to deficiency in micro-nutrients," Milhia Abdul Kader says. "They are coming in a very bad shape."

Speaking to Al Jazeera from a refugee camp in Kenya, Antonio Guterres, the head of UNHCR, the UN refugee agency, expressed grave concern and appealed for "massive aid" to provide the basic necessities.

"I have no doubt that in today's world, Somalia corresponds to the worst humanitarian disaster. I have never seen in a refugee camp people coming in such desperate conditions," he said.

"I saw a mother that had lost three of her children on the way here."

Most of the arrivals to the camps are women and very young children, many of whom are in very bad physical condition, Azad Essa, an Al Jazeera Online Producer in Dadaab reported.

"Every morning hundreds turn up at the registration sites, where they hope to get documented and receive some basic essentials," Essa said.

"But the process is long and people are waiting for days to complete registration and access food, having already walked for days to get here."

The epicentre of the drought lies on the three-way border shared by Kenya, Ethiopia and Somalia, a nomadic region where families depend heavily on livestock.

Uganda and Djibouti have also been hit by the crisis.

Dangerously malnourished

The NGO Save the Children said more than a quarter of children in the worst-hit parts of Kenya are now dangerously malnourished, while malnutrition rates in Somalia have reached 30 per cent in some areas.

According to the UNHCR, Dadaab's three camps now host more than 382,000 people, while thousands more are waiting at reception centres outside the camp.

"The people that are arriving are absolutely desperate," Andrew Wander of Save the Children said.

"They haven't eaten for weeks, they've been travelling for a long, long time in very difficult situations."

Wander said 1,500 people are arriving in Dadaab every day and that the situation is now "extremely serious".

Doctors with Médecins Sans Frontières (MSF) told Al Jazeera the camps are being stretched to capacity.

"The situation in the outskirts of the established camps are catastrophes waiting to happen," Al Jazeera's Essa reported. "There are literally thousands of huts assembled out of tree branches, covered by plastic sheets provided by the UN."

"These refugees have registered, but there is no space for them in any of the three camps, so they have just effectively created their own one," he added.

As well as providing medical help, aid agencies are trying to distribute food and water to the hundreds of thousands of people reaching Dadaab.

The UNHCR's Guterres says they are also trying to provide aid inside Somalia despite al-Shabab's hold on large areas.

"To deliver aid inside Somalia is a very important priority. When we see people in such a desperate situation, it would be much better if they could be supported inside the country."