A ferry carrying nearly 400 passengers capsized in a storm in south-eastern Bangladesh, and police said on Saturday that they feared many were dead.

Up to 100 people swam to shore or were picked up by passing boats after the triple-decked ferry MV Salahuddin went down on Friday night in the Meghna River, local police chief Bakhtiar Alam said.

Two bodies were found floating near the accident site shortly after dawn Saturday, Alam said.

"We will not know how many people have drowned until the ferry is pulled out from under the water," he said.

Hundreds of relatives of passengers on the doomed ferry converged on the scene of the accident on Saturday, some joining search operations with their fishing trawlers.

A local photographer in a nearby village described a middle-aged woman who survived the tragedy crying that she had lost her daughter.

Work on salvaging the sunken steel-bodied ferry was expected to take time as rescuers had not yet located exactly where it went down.

A rescue vessel from state-run Bangladesh Inland Water Transport Corporation was combing the site, 64 km southeast of the capital Dhaka, and another was on its way, officials said.

The ferry sank nearly two hours into the journey from Dhaka to southern Patuakhali, 152 km from Dhaka.

The Meghna is a 210 km river that flows south from north-eastern Bangladesh to the Bay of Bengal. It is an important inland waterway that is heavily travelled by river ferries.

Ferry accidents are common in Bangladesh, a delta nation that is crisscrossed by many rivers. Tropical storms with high winds plague the impoverished country every summer. At least 59 people have been killed in the last week by lighting and flooding in the South Asia nation of 130 million people.

At least 100 people were killed when an overcrowded ferry was caught in a storm in May and sank in the Meghna, and a ferry sinking in the same river in 1986 left at least 224 dead.

Laws penalising those responsible for ferry accidents are rarely enforced in Bangladesh.