It was packed beyond its carrying capacity

Passenger Mohammad Altaf

Hopes are fading for hundreds of people thought to be trapped inside the boat, which now lies under about 20 metres (60 feet) of water in the river Meghna, near the south-eastern port of Chandpur.

River transport authorities said about 150 people were on board the vessel when it sank, but passengers who managed to swim ashore said the total was between 300 and 400.

Survivors say the boat collided with another vessel in stormy weather before overturning.

Up to 70 people escaped from the stricken vessel, which got into trouble shortly before midnight (1800 GMT) on Friday, river authorities said.

Wind and drizzle

Only two bodies have so far been recovered, reports say - a woman and a child.

The two-deck ferry Salahuddin-2 was travelling to the coastal region of Patuakhali from the capital Dhaka 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 it is one of the worst ferry accidents in Bangladesh in recent years and - like many other previous ones - 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.

Onlookers were horrified

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

Divers have been trying to reach the ferry, but there is little to be done until a powerful floating crane arrives from the coastal city of Barisal to lift the ferry out of the water.

Only then will the final death toll become apparent.

Those who survived managed to swim ashore or to reach other boats.

Altaf Hossain, a surviving passenger who managed to swim ashore, said four of his family members including his wife and son were still missing.

He said the ferry was first hit by another vessel from the side and then a strong wind overturned it, although this has not been confirmed.

River travel

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.

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

Ferries are a key means of transportation in Bangladesh. Most accidents are blamed on overloading or on unskilled skippers, correspondents say.

Nearly 200 people were killed when a ferry sank in the Meghna river early last year, and there have been many more smaller ferry disasters.