Some 57,000 people have been forced from their homes because of dramatic floods in south-western Sudan over the past month, health officials say.
Heavy rains have left Aweil, the main town of Northern Bahr al-Ghazal province, largely under water.
A BBC correspondent says the floods pose another challenge to the already delayed voter registration.
Southern Sudan is voting on whether to secede from the north in a referendum in January.
The BBC’s Peter Martell in Southern Sudan says the floods add to the woes of a grossly under-developed region still struggling to rebuild itself after the brutal two-decade war with the north.
“The rains are going to continue up until October, so the situation may get worse,” Southern Sudan’s Health Minister Luka Monoja warned.
“A serious situation has developed in Aweil – more than three quarters of the town is flooded and so many houses collapsed.
“We saw that all the people were chased out of their houses, and were now living on the road, because the road is the only area in the town that is raised.”
Our reporter says the southern government and aid agencies have been working to support those displaced, but the challenge is enormous.
The United Nations has already provided some kind of food assistance to almost half the population of the south this year, he says.
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