"We have a shortage of medicines and we have shortages of workers also," said Viola James, a doctor treating refugees at a transit camp along the border in the Sudanese state of White Nile.
About 5,000 refugees lived in the camp, James said, and she had only five workers to help provide medical aid.
"On top of that we're also helping nearby villages," she said as she checked a young boy suffering from malnutrition.
"There are many malaria cases among the refugees," she said.
South Sudan, the world's youngest nation formed after splitting from the north in 2011, has declared famine in parts of Unity State, saying 100,000 people face starvation and another million are on the brink of famine.
The UN refugee agency UNHCR said tens of thousands of South Sudanese are expected to pour into Sudan in the months ahead.
Sudan already hosts nearly 330,000 South Sudanese who have fled the civil war that erupted in their country in December 2013.
Several transit camps have been set up along the border to receive refugees.
The camp where James works is made up of several tents housing mainly women and children, an AFP correspondent touring the border area said.
