A fishing trawler that sank in the Bay of Bengal on Thursday was packed with illegal migrants bound for Malaysia, dozens of whom are feared to have drowned, Bangladeshi authorities have said.

Rescuers raced to find survivors after the boat went down amid strong waves near the island of Kutubdia in the early hours of Thursday morning. As night fell over the Bay, officials said 42 people had been saved — but added that they did not know how many might still be in the water.

"We have not been able to confirm the total number of passengers who were in the boat," Mohammad Ruhul Amin, deputy commissioner of the town of Cox's Bazar told VICE News.

The fishing boat had started off for Malaysia last night from the Chittagong coast, according to police sources in Cox's Bazar.

Amin said that no bodies had yet been found, and police were questioning individuals suspected to have been running the smuggling operation. "We suspect that three people among those rescued are the human traffickers. We have arrested (them) and have initiated interrogation. We hope to find more information, soon," he added.

Reports varied on the number of passengers the trawler may have been carrying. Sunil Barua, a TV news correspondent in Cox's Bazar told VICE News: "It was a small trawler, ranging between 30 to 35 feet in length. A trawler of that size could not have carried more than 60 to 70 people, huddled together within the limited space."

But survivors said that more than 100 people might have been crammed onto the vessel, according to a coastguard official quoted by bdnews24.com.

Since 2011, more than 670 people are thought to have been killed in similar incidents of overburdened trawlers capsizing in the Bay of Bengal.

The numbers increase each year as thousands of poor Bangladeshis and ethnic Rohingya refugees from Myanmar try to migrate to Malaysia on a perilous 2000-mile journey. Poverty-stricken Bangladeshis and Rohingyas often sell off their property, risking everything in a bid to change their fortunes in the South East Asian powerhouse.

But frequently, they instead meet harrowing ends in the Bay of Bengal.

On November 25, 2011, a trawler carrying at least 180 Bangladeshi workers to Malaysia had capsized in the Bay of Bengal, near Myanmar's Naikkhangdiya coast. Just 19 survived.

On December 14 of that year, a trawler carrying 130 passengers to Malaysia capsized near Saint Martin's island in the Bay of Bengal. While 100 passengers managed to swim to the nearest shore, 25 people went missing. Abdur Rahim, a survivor, informed the media that migrants from Myanmar and Cox's Bazar were on board the vessel.

The flow of Rohingya Muslims has risen with a surge in violence towards the persecuted minority group in Myanmar, beginning with an outbreak of sectarian unrest in 2012. On October 28 of that year, a trawler carrying 130 passengers from Myanmar to Malaysia sank in the Bay. Only a dozen people survived the incident.

A fortnight later, on November 8, 2012, another vessel carrying 110 Rohingya refugees from Myanmar to Malaysia sank near Cox's Bazar. Nearly 85 people, including women and children, are believed to have drowned. Almost 200 Rohingya refugees are thought to have died the following May when their boat sank in a cyclone; only 22 bodies, including 15 children and three women, were ever recovered.

A shipwreck last August gave an insight into the trafficking process. Only one survivor was rescued from the boat, which had been carrying 30 passengers from Bangladesh to Malaysia when it sank in the Bay. The 35-year-old man said that they had all boarded the trawler to go to Malaysia illegally with the help of a human trafficker named Nazrul. Each of these passengers had paid Tk 150,000 (US $ 2,000) to Nazrul for the voyage.

Dr. C R Abrar, executive director of the Dhaka-based Refugee and Migratory Movements Research Unit (RMMRU), explained to VICE News that these sea routes had first been used by the Rohingya refugees from Myanmar. "Over the past few years, poor Bangladeshis began to follow suite, after the Bangladesh government failed to ensure smooth and inexpensive migration process through official channels to Malaysia," he said.

Abrar added that the number of such disasters are on the rise, as "the kingpins behind trafficking rings are never arrested by law enforcement agencies."