Bangladesh has ordered hundreds of thousands of people to leave coastal areas as Cyclone Mahasen approaches.
It is estimated that the cyclone, heading north-east through the Bay of Bengal, will reach land on Thursday.
The Bangladesh Meteorological Department said the storm could create a two metre surge in coastal districts.
Airports in Cox's Bazar and Chittagong are closed until the danger subsides.
Myanmar (Burma) is also threatened. More than 100,000 people died in 2008 when Cyclone Nargis devastated many coastal villages there.
Associated heavy rain has caused floods and mudslides which killed at least seven people, according to the disaster management centre in Sri Lanka.