Cyclone Mora is likely to move in a northerly direction further, the BMD said. One of the six people died of a heart attack during the storm, while others were killed by falling trees and houses in Cox's Bazar and Rangamati, local media reported.
Under Cyclone Mora's influence, strong winds with rain and thundershowers were continuing over North Bay, coastal districts and maritime ports of Bangladesh, the Daily Star reported.
"Wind speed is estimated at 130 kmph in Saint Martins Island and 150 kmph at Cox's Bazar port after it hit the area between 6 am and 7 am," weather official AKM Nazmul Haque said.
All flights to and from Chittagong international airport and Cox's Bazar airport were suspended. At least three lakh people have been taken to shelters in more than 10 districts most vulnerable to Cyclone Mora, BD News quoted Additional Secretary Golam Mostafa, a spokesman for the disaster management ministry's control room, as saying.
"The people were moved out to at least 400 cyclone shelters or safer places like schools and government offices in the coastal areas," a disaster management ministry spokesman said.
There are also concerns over thousands of Rohingya refugees living in makeshift homes after fleeing violence in neighbouring Myanmar. At least 2.5 million people in 10 districts risk coming in the way of Cyclone Mora.
The districts at risk were Cox's Bazar, Chittagong, Noakhali, Lakshmipur, Feni, Chandpur, Barguna, Patuakhali, Bhola, Barisal and Pirojpur. Prime Minister Sheikh Hasina was monitoring the situation from Vienna, where she has gone to attend a conference on atomic energy.
"The prime minister is maintaining round-the-clock communication with Dhaka on the storm situation. She has ordered all-out preparation to tackle the storm," said Ihsanul Karim, the prime minister's press secretary.
Under the influence of the cyclonic storm, low-lying areas of the coastal districts and their offshore islands were likely to be inundated by a storm surge four- or five-feet high above normal astronomical tide, the BMD said. All fishing boats and trawlers in the North Bay and far out in the sea have been asked to take shelter till further notice.
The BMD issued the highest level of warning signal in a scale of 10 for two ports after Cyclone Mora developed into a severe cyclonic storm. Habibur Rahman, a member of Saint Martin's Island Union Parishad, told Bangladeshi daily Prothom Alo that several houses were damaged in the island today morning.
Bangladesh is often hit by storms between April and December, causing deaths and widespread destruction. Cyclone Roanu hit the southern coast of Bangladesh last year, killing 20 people and forcing half-a-million to flee. Mora Cyclone formed after heavy rains in Sri Lanka caused floods and landslides killing over 180 people.