In dramatic images taken moments after they crashed into one another, horrified residents can be seen watching from the riverbank as small boats raced out in a bid to rescue passengers.
It was not immediately clear how many were saved or what caused the accident between the two boats which were loaded with people and goods.
Rivers are key to transport in the vast central African country which has a very poor road infrastructure.
Deadly boating accidents occur frequently as crews often overload the vessels.
Most river traffic is run by small informal operators, and officials have warned that adherence to maritime regulations is poor.