The death toll from a boat accident in Bangladesh has risen to 24, with rescuers pulling six more bodies from the river as they wrapped up the search operation on Friday, police said.

Rescuers found the bodies floating in the river after the boat was salvaged from the Shandhya River in the southern district of Barisal, SM Akhteruzzaman, the district police chief, told DPA by phone.

The engine-propelled boat, ML Oishi, went down on Wednesday with roughly 60 passengers on board as it was about to anchor at Dasherhaat station, some 110 kilometres south of the capital Dhaka.

Most of those on board were able to swim ashore while five passengers were rescued, said Akhteruzzaman, adding that the rescue operation had formally ended on Friday morning.

Many of the boats plying Bangladesh's waterways do not maintain passenger registers and accidents are frequent.

While the government has launched an investigation into the accident, an official at the Barisal Port Authority said the boat had been overcrowded.

In February 2015, at least 70 people died after a double-decker ferry was hit by a cargo vessel and capsized in a river in central Bangladesh.

Forty-nine people were confirmed dead after a ferry carrying more than 200 passengers sank in the Padma River in August 2014.

And nearly 150 people were killed in March 2012 after an overcrowded ferry carrying about 200 passengers sank in central Bangladesh when it was hit by an oil tanker.