A passenger boat believed to be carrying up to 40 passengers sank in the Teesta River in Burirhat area under Rajarhat upazila on Sunday morning.
The boat, bound for Sitabkhan from Burirhat, sank around 11:00am," said Upazila Nirbahi Officer (UNO) Md Rashedul Haque, adding, during the capsize, there were strong currents in the river.
It is unclear how many people were aboard the boat but Gharialdanga Union Parishad chairman Rabindranath Karmokar said a boat usually ferries 35 to 40 passengers at a time.
It was not immediately clear if anyone has died.
Divers of Fire Service and Civil Defence have started the rescue operation.
Thousands of people, including relatives of many of those missing, have gathered on the banks of the river.