UN officials returning from a border town in Central African Republic say around 9,700 people have crossed over from Sudan so far and that they expect more to come.
About a third of them were Central Africans returning home.
Some have been taken in by local families whilst other have had to form makeshift camps around the town of Am Dafok.
"We are currently discussing with the minister who will decide on behalf of the government where this population will be settled," said Mohamed Ag Ayoya, the UN's top humanitarian official in the country.
Conditions in Am Dafok town are far from ideal as the rainy season started this month and the region is prone to flooding.
Outbreaks of disease, in particular malaria are worrying the World Health Organisation (WHO). And malnutrition is a concern too, if people get weak from it they will be all the more prone to getting sick.
"We are already starting to take care of the sick, at least in relation to this. We are trying to see if we can provide mosquito nets so that people can at least protect themselves against malaria," Gervais Tengomo, an emergencies officer with the WHO said.
"We are also intensifying surveillance to be able to quickly detect a possible epidemic and to be able to control it as quickly as possible," he added.
Central African Republic has many troubles of its own. The UN say more than half the population is "in need of assistance and protection."
It's been enduring its own civil war for several years which has kept it amongst the ten poorest countries in the world.
The UN says around 120,000 people also need food assistance there.