A total of 479 cyclone shelters have been opened in Chattogram as part of efforts to fight cyclone Bulbul.
Also, people can take shelter in 4,000 educational institutions in emergency situations, authorities said.
"The local authorities are announcing on loudspeakers to alert the people," said Chattogram District Administration Staff Officer Tanvir Ahmad Shamim.
He said medical teams are ready to serve the victims and control rooms have been opened to monitor the situation.
Chattogram Deputy Commissioner Md Elias Hossen said the coast guard, the army and the navy will work jointly to fight the cyclone.
"Activities at Chattogram Shah Amanat International Airport are still normal and no flight schedule has been changed due to the cyclone," said Wing Commander Sarwar-E-Zaman, manager of the airport.
The airport authorities have taken all-out preparations to fight the disaster, he added.
It has been drizzling in different parts of Chattogram ahead of the cyclone.
Chattogram Port Secretary Omor Faruk said, "Apart from the danger signal number 9 of the Met office, Chattogram port has also issued its own red alert number 4."
"Moreover, all operational activities of the port have been halted," he said.
He said ships and small vessels in the Karnaphuli river port channel have been transferred to the upstream of the Shah Amanat Bridge.
Big ships in the ocean are being transferred to Kutubdia and Cox's Bazar coastal areas and the authorities concerned have been ordered to keep the ship engines running.
The authorities concerned have taken sufficient security measures for ensuring the safety of the tourists who are stranded in the St Martin's island ahead of Bulbul.