Hundreds of thousands of people have been evacuated from the path of a cyclone careening towards densely populated, low-lying Bangladesh, according to officials.

About 33,000 Rohingya refugees from Myanmar, controversially relocated to a storm-prone island in the Bay of Bengal, were advised to remain indoors.

Cyclones - the equivalent of hurricanes in the North Atlantic or typhoons in the Northwest Pacific - are a regular and deadly menace on the coast of the northern Indian Ocean where tens of millions of people live.

But scientists say climate change is likely making them more intense and frequent, and Bangladesh is already rated by the UN as one of the countries most affected by extreme weather events since the turn of the century.

Cyclone Sitrang, packing gusts of 88km/h, was forecast to make landfall near the southern Bangladeshi town of Khepupara by tomorrow, the country's weather office said.

Most worrying for authorities was the predicted storm surge of up to three metres above normal tide levels, which could inundate areas home to millions of people.

The government plans to evacuate about 2.5 million people from the most vulnerable areas in the path of the storm before the cyclone hits, the country's disaster management minister Enamur Rahman told reporters.

"The evacuation has already begun from the morning," the minister said, adding that more than 7,000 shelters have been readied in an effort to keep casualties to a minimum.

At least 250,000 people had already been evacuated from coastal districts to cyclone shelters by the afternoon, two regional administrators told AFP.

Tens of thousands of volunteers have been mobilised for the effort, said a spokesman for the local chapter of the Bangladesh Red Crescent Society.

A 40-year-old woman was killed in the rural town of Lohagara after she was hit by a branch of a tree, which fell in gusty winds, a local official said.

The Red Crescent Society has mobilised tens of thousands of volunteers to alert people using loudhailers and help villagers evacuate, a spokesman said.

The newly formed silt island of Bhashan Char, where Bangladesh has been relocating Rohingya refugees to alleviate overcrowding in their refugee camps, was also expected to be hit by heavy rains and strong winds.

In the neighbouring eastern Indian state of West Bengal, several thousand people were also being evacuated as a precaution, with more than 100 relief centres opened, officials said.

In 2020, Cyclone Amphan, only the second "super cyclone" ever recorded over the Bay of Bengal, killed more than 100 people in Bangladesh and India, and affected millions.

Last year, more than a million people were evacuated along India's east coast before Cyclone Yaas battered the area with winds gusting up to 155km/h - equivalent to a Category 2 hurricane.

The 1970 Bhola cyclone, one of the world's worst natural disasters, killed several hundred thousand people in Bangladesh - then known as East Pakistan - and India.

In recent years, better forecasting and more effective evacuation planning have dramatically reduced the death toll from such storms.