The incident occurred around 11:30pm on Wednesday
Police said the accidents were reported on Saturday morning from the coastal district Sadar and Chakoria Upazilas.
Chakoria police camp chief Sub Inspector Abul Hashem said a road crash around 9am at Harbang Dayal area killed four passengers of a car on the spot.
Another accident on the highway near the district town has left one person killed.
Chiringa Highway Police OC Md Abul Kalam Azad said a pick-up truck met with an accident on the Cox's Bazar-Chittagong Highway at Rashidnagar around 7am.
Two of the victims died after being taken to the local hospital, said the police officer.