The "very dire" humanitarian crisis in Somalia is the worst in Africa for many years, says Oxfam's coordinator for the failed Horn of Africa state.
Many of its hundreds of thousands of internally-displaced people, the world's largest such concentration, have little food or shelter, he said.
Mogadishu civilians have been fleeing intense fighting between opposition fighters and pro-government forces.
The exodus is continuing from the capital amid the crackle of gunfire.
The BBC's Mohamad Olad Hassan in Mogadishu says city-dwellers are taking advantage of a relative lull in the fighting on Tuesday to get out, carrying light belongings in the arms.
Many thousands of people, mainly women and children, have fled to the outskirts of the city where most are sheltering under trees with little to eat or drink, he says.
Hassan Noor, Oxfam's humanitarian coordinator for Somalia, told the BBC's Network Africa program circumstances in the capital were "very dire".
"The situation is really appalling," he said.
"There are hundreds of children all over the area with tubes on their faces and [saline] drips on their hands. Some of them are actually unconscious and suffering from all sorts of diseases, mainly acute diarrhea and cholera."
"I have seen the situation in Darfur, northern Uganda, some parts of Congo, but what is actually happening now in Somalia is indeed the worst kind of humanitarian situation in Africa in many years," he added.
Opposition fighters from Hisbul-Islam and al-Shabab groups have been locked in see-sawing battles in the Somali capital with pro-government forces that have displaced more than 60,000 civilians since 7 May.
Loyalist troops in north Mogadishu retook a police station which had been occupied by fighters for the past month. The police station is seen as the key to controlling that area of town.
However, at least five Somali policemen were killed in a roadside bomb blast in the south of the capital.
There are 4,300 African Union peacekeepers from Uganda and Burundi in the capital to help bolster the government, but they do not have a mandate to pursue the fighters.
The UN last month warned that drought had left nearly half of Somalia's nine million population malnourished and some 3.2 million in urgent need of food aid.
It is estimated at least one million people have been internally displaced by almost perpetual civil conflict in the failed Horn of Africa nation since the collapse of its central government in 1991.
PHOTO CAPTION
An opposition fighter opposed to the Somali government in Mogadishu on May 17.
Source: BBC