The deceased included: Reena Begum, 35, Ziaul Haque, 50, Obaidullah, 30, and Bachchu Mia, all residents of Autarak Chhara in the upazila.
Locals said lightning struck the engine-driven boat near Maini Bazar in Langdu upazila when they were returning home from the market. All the three victims of the incident are residents of Bhasaindam union.
Langdu Police Station Officer-in-Charge (OC) Harunur Rashid confirmed the incident and said three people on a boat were killed when lightning struck them while returning from Maini Bazar and another woman also died when lightning struck them.
He said two cases of unnatural death would be registered in connection with these incidents.