According to forest officials and pilot of the coaster, Sea Horse-1, the incident happened in the river near Harintana on Saturday afternoon.
A tanker, OT Southern Star 7, had sunk in the same river in December 2014 spilling 357,664 litres of furnace oil it had been carrying.
The massive oil spill from the tanker had put the biodiversity and ecology of the Sundarbans, world's biggest mangrove forest and a world heritage site since 1997, at risk.
Since then environmentalists and different socio-cultural organisations have been demanding a halt to plying of water vessels through the Sundarbans.
Sea Horse-1 pilot Md Sirajul Islam Molla told bdnews24.com that the coaster had stated for Noaparha in Jessore from Chittagong on Mar 16.
He said, “The bottom (of the vessel) suddenly ruptured when it reached Harintana area.”
A tanker, Noorjahan-1, rushed and rescued the coaster’s crew members, he added.
Sundarbans Divisional Forest Officer (South) Saidul Islam said the vessel had sunk 25 nautical miles off the Sundarbans’ Chandpai range office.
He said forest department people could not reach the spot on Saturday. “Steps will be taken to recover the coaster on Sunday after contacting its owner,” he added.
