A bus hit an auto-rickshaw in Bhanga area of Dhaka-Sylhet Highway in the evening.
Three of the deceased were identified as auto-rickshaw driver Juned Mia, 28, Karima, 4, and Arfa, 12, while identity of their mother could not be known immediately.
Officer-in-Charge of Osmani Nagar Police Station Shaymal Banik said a Sylhet-bound bus of Mamun Paribahan collided with a Sherpur-bound auto-rickshaw killing two of its passengers on the spot.
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Later, two other passengers died while being taken to the hospital.
The injured are being treated at the Sylhet MAG Osmani Medical College Hospital, the OC said.