Hundreds of thousands of people are being evacuated from coastal areas of Bangladesh threatened by Cyclone Mahasen.
The country's National Planning Minister, Tin Naing Thein, said more than 150,000 people had been relocated to higher ground. The government said a fifth of those were Rohingyas.
The Bangladesh Meteorological Department said the storm could create a surge 2m high in coastal districts and residents are being urged to make for cyclone shelters.
But the UN still described it as "life-threatening" for 8.2 million people in Bangladesh, Burma and north-east India.
More than 100,000 people died in 2008 when Cyclone Nargis devastated many of Burma's coastal villages.
(Reuters) - Authorities in Myanmar struggled on Wednesday to evacuate tens of thousands of people, most of them Rohingya Muslims, before a cyclone reaches camps in low-lying regions that have been their home since ethnic and religious unrest last year.
Cyclone Mahasen has already killed at least seven people and displaced 3,881 in Sri Lanka, its Disaster Management Center said on Tuesday.
The storm is moving north over the Bay of Bengal and is expected to reach land on Thursday, hitting north of Chittagong in Bangladesh.
The Myanmar government had planned to move 38,000 internally displaced people, most of them Rohingya Muslims, by Tuesday but many have refused to relocate from camps in Rakhine State in the west of the country, afraid of the authorities' intentions.
Cyclone Mahasen has begun crossing Bangladesh's southern coast, as people packed into evacuation shelters.
The storm hit Patuakhali district on Thursday with winds of up to 100km/h (60mph), and was heading for the ports of Chittagong and Cox's Bazar.
One person has been reported dead, Bangladeshi officials say.
Hundreds of thousands of people have been ordered to evacuate low-lying areas in Bangladesh and Burma, and take shelter in cyclone centres.
The Bangladeshi authorities have raised the danger level to seven out of 10 for low-lying areas around Chittagong and Cox's Bazar.
However, Shamsuddun Ahmed, deputy director of Bangladesh's Meteorological Department, told AFP news agency the cyclone was not expected to cause serious damage as it was "not severe".