Emergency workers rescued about 32 Bangladeshis in the Bay of Bengal after the boat capsized some 2.5 kilometres (1.5 miles) offshore, police and the coastguard said.
Several passengers also managed to swim to shore, but dozens of others were still unaccounted for, although the exact figure was not known, coast guard commander Maruf Hassan told AFP.
“We have heard from passengers that up to 70 passengers were on board when it capsized. We have rescued 32 and several others have floated to shore,” Hassan said.
Estimates varied on the total number of passengers, with police saying 60 were on board, but private TV station Somoy putting the figure as high as 100.
The boat hit strong currents in a treacherous sea channel shortly after leaving a coastal town near the southern port city of Chittagong, Hassan said.
It sank near the Bangladeshi island of Kutubdia where coastguard officers and police were now scouring the waters for victims.
“It’s a small fishing trawler which was overloaded. It sank as it tried to make a turn in a dangerous channel near the Kutubdia island,” Hassan said.
The boat had been attempting to make the dangerous voyage to Malaysia, a common destination every year for thousands of impoverished Bangladeshis and ethnic Rohingya refugees from Myanmar.
“All the passengers are Bangladeshi and they were heading to Malaysia by sea illegally,” local police chief Masud Alam said.
Hassan said two coast guard ships and two smaller boats were leading the rescue efforts, while fishing trawlers have also been asked to help search the waters.
“Fortunately one of our ships was stationed nearby when the boat first listed and then sank early Thursday morning,” Hassan said, adding that those rescued people were being treated for minor injuries.
Rights groups say thousands have perished attempting the 3,200-kilometre (2,000-mile) journey, with many falling into the hands of people-traffickers.
Some 100 Rohingya refugees lost their lives in two boating tragedies off the Bangladesh coast in October and November 2012.
Bangladesh’s coastguard and border forces have launched crackdowns on economic migrants, while also arresting a number of human traffickers and confiscating their ships. But there has been no noticeable impact.
The migrants are illegal because they do not travel with the proper visas and attempt to enter Malaysia without notifying authorities.
Ferry and other boating accidents are common in Bangladesh. Officials have said more than 95 percent of the country’s hundreds of thousands of small and medium-sized boats do not meet minimum safety regulations.
Some 50 people were killed in August last year when a crowded ferry sank in rough weather in Bangladesh’s Munshiganj district. (AFP)