Navy divers have been brought in to help in the search

Divers are now busy tying ropes to the ferry which lies under about 20 metres (60 feet) of water.

Only 11 bodies have been recovered so far.

Survivors have said the vessel was seriously overcrowded - carrying more than 300 passengers rather than the 150 the river transport authorities say were aboard.

Up to 100 people escaped from the stricken vessel - but hopes are fading for the hundreds of people thought to be trapped inside.

Survivors say the boat collided with another vessel in stormy weather before overturning in what appears to be one of Bangladesh's worst ferry disasters.

Wind and drizzle

The final death toll will not be known until the ferry is pulled out of the water.

A large crowd of relatives and onlookers gathered on the banks of the river in the hope of finding more survivors - but rescue workers said that was unlikely.

The two-deck ferry Salahuddin-2 was travelling to the coastal region of Patuakhali from the capital Dhaka on Friday when it was struck by a whirlwind - a common phenomenon at this time of year.

"It was packed beyond its carrying capacity," passenger Mohammad Altaf told the Reuters news agency.

"It was dark and we were sitting on the ferry's congested upper deck. It was drizzling, then came the strong winds and the ferry listed to one side," he said.

"Within moments I was thrown overboard into the water and I saw the ferry going down as well," he told Reuters.

The BBC's Alastair Lawson in Dhaka says that like many other previous ferry accidents in Bangladesh, this one could have been avoided.

Inadequate safety

The boat lacked adequate escape procedures in the event of an emergency and trapped survivors may have died because the nearest rescue boat lacked the proper equipment.

Most Bangladeshi ferries travelling on local routes do not keep passenger lists or issue tickets.

Ferry accidents are very common in Bangladesh, a country criss-crossed by hundreds of rivers.

Most accidents are blamed on overloading or on unskilled skippers, correspondents say.

Friday's disaster occurred near the powerful confluence of three major rivers - the Padma, Meghna and Jamuna - which flow into the Bay of Bengal.