The boat sank as it was carrying a large number of people returning from a fair at Kalna in Burdwan district to Shantipur in Nadia district last night, Burdwan Superintendent of Police Gaurab Sharma said.
While many people swam to safety, five persons were missing, he said, adding divers were pressed into service to locate them.
The situation turned violent this morning when family members of the missing persons and locals gathered on the other side of the river at Shantipur and a mob set ablaze seven boats in protest against alleged delay in rescue operation, Nadia Superintendent of Police Sheesram Jhajharia said.