Local authorities said the fire erupted in the three-storey "Obhijan-10" river ferry with nearly a thousand passengers and crew members on board following a "possible explosion in the engine room" at around 3 am. local time (GMT+6) on Friday in Jhalakathi, 250 kilometres (160 miles) south of the capital Dhaka. 

The launch was ferrying passengers to Barguna from Dhaka via Chandpur, Barisal and Jhalakathi, according to local media reports.

Officials in the Bangladesh fire service's control-room said they had been informed about the fire at 3:28 am. local time and firemen had launched firefighting and rescue operations at the scene from 3:50 am. Bangladesh time.

Firefighters said the massive blaze was brought under control at around 5:20 am. local time.

Rescuers said at least 40 passengers of the launch have been killed — most of them died from the fire and a few by drowning as many people jumped into the river after the blaze had erupted — while more than 70 people injured in the accident have been admitted to local hospitals.

Health officials said the death toll could climb as several passengers of the ferry are undergoing treatments with life-threatening burn injuries. 

Local authorities said a large number of passengers had jumped into the river after the ferry caught fire, and few of them are still missing.

A survivour claimed he had heard a loud explosion in the engine room before the blaze erupted.

Senior officials of the Bangladesh government said two investigation committees have been formed to probe into the cause of the deadly ferry fire.