The storm caused by a tropical depression in the Bay of Bengal moved slightly north-northeastwards and was about 555 kms southwest of Chittagong port, 500 kms southwest of Cox’s Bazar port and 445 kms south-southwest of Mongla port at midnight.
The bulletin said that maximum sustained wind speed within 54 kms of the storm centre is about 62 kph rising to 90 kph in gusts/ squalls.
A 6:58pm bulletin had said the cyclone may sweep the coast at dawn and had travelled 175 kilometres in nine hours on Wednesday.
The lastet bulletin said the sea will remain very rough near the storm centre.
Maritime ports of Chittagong and Cox’s Bazar have been advised to keep hoisted the danger signal number ‘7’.
The coastal districts of Cox’s Bazar, Chittagong, Noakhali, Laxmipur, Feni, Chandpur, Bhola, Borguna, Patuakhali, Barisal and their offshore islands and chars will come under danger signal number seven.
Maritime port of Mongla has been advised to keep hoisted danger signal number five.
The coastal districts of Pirozpur, Jhalokathi, Bagherhat, Khulna, Satkhira and their offshore islands and chars will come under danger signal number five.
Under the influence of the storm the low-lying areas of the coastal districts of Cox’s Bazar, Chittagong, Noakhali, Laxmipur, Feni, Chandpur, Barguna, Bhola, Patuakhali, Barisal, Pirojpur, Jhalokathi, Bagherhat, Khulna, Satkhira and their offshore islands and chars are likely to be inundated by storm surge of 8-10 feet height above normal tide.
Cox’s Bazar, Chittagong, Noakhali, Laxmipur, Feni, Chandpur, Barguna, Patuakhali, Barisal, Bhola, Pirojpur, and their offshore islands and shoals are likely to experience wind speed up to 90-100 kph in gusts/ squalls.
Jhalokathi, Bagerhat, Khulna, Satkhira and the islands and chars are likely to experience wind speed up to 80-90 kph in gusts/ squalls.
Due to very heavy rainfall, landslide may occur at places over the hilly regions of Chittagong division.
All fishing boats, trawlers and marine vessels over north Bay have been advised to remain in shelter until further notice.
Massive preparations have been taken in villages, unions and Upazilas of the coastal belts to tackle the cyclone. The people of the coastline started running for safety amid an escalating panic as the Met Office issued overnight Danger Signal No 7.
Leave has been cancelled for all government officials and employees in the coastal areas.
Met Office Director Shah Alam Bhuiyan said that the transitional speed of Mahasen was 20 kms per hour. "The speed may rise after it comes closer to the coastline. If the cyclone approaches this way, heavy downpour and tide may occur in the coastal areas of Cox's Bazar, Chittagong and the adjourning areas."
The storm has already killed at least seven people and displaced 3,881 in Sri Lanka, its Disaster Management Center said on Tuesday.
A boat carrying about 100 Rohingya Muslims capsized off western Myanmar with some 50 feared drowned at the start of a mass evacuation from low-lying regions ahead of the approaching storm.
An UN agency warning says that more than 8 million people of Bangladesh, India and Myanmar could be in danger due to the storm.
The authorities of Shah Amanat International Airport, Chittagong Port and Cox's Bazar Airport shut down operations on Wednesday morning.
Bangladesh Inland Water Transport Authority (BIWTA) grounded vessels and ferries on 38 long routes of the southern part until further notice.
All factories at the Chittagong Export Processing Zone (EPZ) were closed down until the storm wears off, Bangladesh Export Processing Zones Authority (BEPZA) General Manager Abdur Rashid told bdnews24.com.
SM Abdul Kader, Additional Deputy Commissioner of Chittagong, who is working as the Convener of the Cyclone Preparatory Committee, said: "We've already started evacuating the people living in the risky areas of Sandwip and Banshkhali. We've been informed by the district administrations that the residents of the low-lying coastal areas in Patuakhali, Cox's Bazar and Noakhali districts are being moved to safety."
It was drizzling in the coastline since Wednesday morning.