There were over 50 people in the boat when it capsized in Sandya river amid strong currents.
"So far, 13 bodies, including five of women and a minor, had been recovered," police Assistant Superintendent Motaleb Hossain said.
"Many passengers of the sunken boat are still missing," an official in coastal Barisal district said.
He said fire service divers with assistance of police and people in the neighbourhood were carrying out rescue efforts.
A fire service official said that their divers have located the sunken vessel and were preparing to look for more bodies feared to be trapped inside.
Ferry accidents are common in Bangladesh, criss-crossed by over 300 rivers while many of them turn turbulent during the monsoon time.
In February last year, 69 people died in central Bangladesh in a boat mishap.
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