Bangladeshi authorities are trying to evacuate up to a million people before a powerful cyclone makes landfall.
Cyclone Mora is likely to hit the eastern coast early on Tuesday, the meteorological department said.
Port cities in the south-east have been asked to display the highest warning system known as “great danger level 10”. Ports further west are on level 8.
The cyclone formed after heavy rains in Sri Lanka caused floods and landslides that killed at least 180 people.
The worst flooding in 14 years on the island has affected the lives of more than half a million people. More than 100 people remain missing.
In Bangladesh, people in Chittagong district have been flocking to nearly 500 cyclone shelters as warnings were announced on loudspeakers.
Schools and government offices are being used to shelter people, and residents of hilly areas are also being urged to evacuate.
Low-lying areas of Cox’s Bazar, Chittagong and many other coastal districts are “likely to be inundated” by a storm surge of 1.2m-1.5m (4-5 feet) above normal levels, the meteorological department warned.
“We are targeting zero casualties and we will try our best to evacuate more than a million before the landfall,” disaster management authority spokesman Abul Hashim told the AFP news agency.
He said nearly 300,000 people had already been moved to cyclone shelters.
Though Bangladesh is used to cyclones, many people don’t live in dwellings sturdy enough to withstand bad weather, the BBC’s South Asia editor Charles Haviland says.
Their lives, and the crops on which so many of them depend, he says, are constantly at risk when cyclones hit.
Fishing boat and trawlers have been advised to remain in port, and coastal ferries have suspended operations.
Bangladesh is yet to fully recover from flash floods in the north-east of the country in April that destroyed rice crops and pushed rice prices to record highs.
Heavy rains are also expected in parts of north-eastern India due to Cyclone Mora.