A cargo vessel carrying coal capsized at Pashur Channel near Mongla port of Bagerhat on Saturday night.
Twelve navigators of the sunken cargo have been rescued after the incident.
However, the regular activities of Mongla port were not hampered due to the accident, said the port authority.
Osman, master of the sunken cargo informed that they were going towards Mongla port from Harbaria carrying coal, but it collided with another cargo near at Baniasanta area and water started leaking into the vessel.
At a stage, the cargo was lifted into a char and all safely got off.
Then, it gradually sunk into the river.
Fakhar Uddin, Harbor Master of Mongla Port Authority, said, "As one of our ships was leaving the channel in the morning, found a coal-laden ship named BB-1148 in a half-sinking position.
He added that the ship was in a semi-submerged condition in the Pashur River in the area called Chila of Esmail, one kilometer south of Mongla port.
"All the sailors in the ship are safe and healthy and we are trying to contact the ship owners.
Arrangements will be made to quickly remove the ship from the channel," Fakhar uddin said.
However, he could not confirm the amount of coal in the ship.