The accident occurred when the train was crossing a bridge at Baramchal in Kulaura around 11:50pm on Sunday, snapping rail links between Sylhet and the rest of the country, railways officials and locals said.
Intercity Upaban Express left the Sylhet station at 10pm and reached Maijgaon station safely. Then it crossed Bhatera and the five coaches went off the track only after it crossed 200 metres from Baramchal station, said Srimangal Station Master Jahangir Alam.
One of the coaches crashing the culvert fell into a canal and two bogies rolled into the field beside the rail tracks.
Three among the dead were women and the other a man, Kulaura Police Station chief Yardous Hasan told bdnews24.com.
Resident Medical Officer Dr ‘Zakir’ at Kulaura Health Complex said there were four dead bodies at the government facility from the accident.
They treated 65 people injured in the accident until 3:20am on Monday, the doctor said.
Eighteen of the injured were sent to the Moulvibazar General Hospital and Sylhet MAG Osmani Medical College Hospital in “critical condition” for life-saving treatment, he added.
Witnesses said they saw a family taking a body away from the scene, but there was no official confirmation.
Earlier, Kulaura Police Station OC Yardous Hasan said the damaged coaches of the train were disconnected from the engine before they fell off the tracks.
Apart from the five damaged bogies, one was seen undamaged at the site.
Trains including Kalni Express, Jayantika Express, Surma Mail, Parabat Express got halted after the accident, according to the Srimangal Station master and Shamser Nagar Station Master Kabir Hossain. Some of the passengers got off the train and tried to reach their destination by alternative ways.
All the 17 bogies of the Upaban Express were full of passengers, they said.
An injured passenger told bdnews24.com that he, along with his brother and father, was in the coach that fell into the canal. The train began to sway after crossing Baramchal making their coach lopsided and falling into the canal after it reached the culvert, he said.
The railway authorities have formed two separate panels to investigate the accident.
Photos and videos believed to be of the scene and posted on social media showed several damaged coaches of a train lying on their sides with at least one compartment overturned as hundreds of onlookers gathered there.