Medecins Sans Frontieres warns that people are dying in large numbers in a refugee camp in South Sudan, especially children under five.
MSF says on an average day in Batil camp, three or four children will die.
The BBC reports the rainy season makes it impossible to bring food in by road, and the only way to deliver aid is by air.
Some 120,000 refugees have fled to camps in South Sudan from Sudan following fighting north of the border.
"What we are seeing here in this camp in nothing short of a humanitarian catastrophe," MSF's medical co-ordinator Helen Patterson says.
The majority of those who have died in the camp are children under five, and diarrhoea seems to be the biggest cause, with malnutrition is a contributing factor, calling for urgent help.
Refugees - many of whom walked to weeks to get to camps - told the BBC that they were forced from their homes in South Korofan and Blue Nile State by ground and air attacks by the military.
Officials in Khartoum deny that civilians are being targeted.
MSF nurse Vanessa Cramond of New Zealand, who is working in Upper Nile State, says many refugees were unprepared.
"They didn't even have the normal buckets and shelter or blankets that they might have had at home Large numbers of people with dehydration and diarrhoea from the journey because they were unprepared and because the walk has taken some time," she told the ABC.
"We've seen a huge amount of diarrhoea, a huge amount of skin infection, a huge amount of eye infection, which tells us that their ability to drink and wash and maintain their own hygiene is really limited.
"Alongside that there's been a huge amount of vulnerable children in this group so we've also been treating severe malnutrition".