"All the deaths were reported from the southwestern coastlines where the cyclone hit with its maximum strength before being weakened gradually," a disaster management ministry spokesman told PTI.
Officials from coastal areas earlier reported the deaths mostly from offshore islands of southwestern Barisal region with the highest toll recorded in Barguna district, the worst affected area where the storm levelled hundreds of thatched houses and standing crops and uprooted trees.
The cyclone first struck the southern Patuakhali coast with wind speed up to 90 kilometres per hour, but it gradually weakened into a tropical storm and then dissipated, causing far less damage than had been feared.
"The cyclone gradually lost its strength as it headed towards India's Tripura state crossing (Bangladesh's) Bandarban (hill district) this afternoon," meteorology department's deputy director Shamsuddin Ahmed told PTI.
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MeT office director Shah Alam earlier said the Mahasen first hit the Khepupara of Patuakhali and then it proceeded towards the Noakhali and Chittagong Coast through the confluence of the Tentulia and Meghna rivers.
Authorities earlier had evacuated over one million people and sent to 1,365 shelters stretching across the southern coastlines after the MeT office issued Danger Signal no 7 in a scale of 10 late yesterday.