"The rains on the night of Monday to Tuesday have caused at least 50 deaths," the governor said, as quoted by Daily Sabah.
He added that the bodies of more victims may have been buried in the mud.
According to local authorities, over 1,000 houses were flooded in the city of Boma, near the border with Angola, and some 10,000 people have been left homeless.
A crisis task force has reportedly been set up to assist those affected.
The Kalamu river, which flows through the city of Boma, burst its banks on Tuesday due to torrential rain.
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