A small ferry has capsized in the Megna River near the Bangladeshi capital, Dhaka.
Officials say two bodies have been recovered so far. Many people are believed to have been rescued but some reports say dozens are still missing.
However it is unclear exactly how many people were on board the MV Sarosh - estimates range from 60-100 people.
Ferry accidents are common on Bangladesh's vast river network and scores of people are killed every year.
Such incidents are often blamed on overcrowding and poor quality of the boats, which are the main form of travel in some rural parts of the country.
In March last year, more than 112 died when a ferry on the wide and fast-moving Meghna River collided with an oil tanker and sank.
In this latest incident, local media said the MV Sarosh was hit by another vessel which was transporting sand. Reuters quoted officials as saying the ferry had not been overloaded.
Local police chief Jahangir Hossain told the AFP news agency: "So far we have gathered that the ferry was carrying around 100 people. A maximum 40 people are feared missing."
Dozens of people were reportedly rescued or swam to shore.