Bangladesh was battered by a super-cyclone yesterday, with winds of about 150mph (240km/h) - some of the worst on record in the region. At least 28 fishermen were feared drowned.

As Cyclone Sidr slammed into the southwestern coast, destroying thousands of houses, 650,000 villagers fled to shelters. Officials said that another 3 million people would have to be moved. In the coastal districts of Barguna, Bagerhat, Barisal and Bhola thousands of flimsy straw and mud huts were flattened as the cyclone flooded lowlying areas and uprooted trees and electricity and telephone poles. Road, rail and river transport was also affected.

"From my window, I can see tins ripped off the roofs and tree branches flying under the sky [which is] covered with thick clouds," Moulvi Feroze Ahmed, a local government official on St Martin's island in the Bay of Bengal, said. "It looks like the sea is coming to grab us."

Bangladesh has the worst record of cyclone storm surges in the world. As cyclones sweep up the Bay of Bengal, the funnel shape of the coastline squeezes storm surges over a very low coastline. The warm seas in the Bay of Bengal are also a notorious breeding ground for cyclones, particularly at this time of year, when clusters of thunderstorms can turn into a ferocious, rotating storm.

As storm surges overwhelm the coastline they tear through a labyrinth of waterways in the enormous river deltas. The region is densely populated, with many people living on chars - islands of sand and silt that gradually shift with the surrounding waters. Much of the land is barely a metre above sea level and one third of Bangladesh lies less than six metres above.

These vulnerable people are also among the poorest in the country. Although great efforts have been made to give good storm warnings and build cyclone shelters on higher land, this is still inadequate for the estimated five million people in the high-risk areas.

However, the situation has improved since the catastrophic storm surge of November 12, 1970, when at least half a million people died in what was the worst natural disaster of the 20th century. About 8,000 sq km (3,090 sq miles) of land was devastated, with almost all buildings and crops obliterated. The chaotic rescue operation helped to fuel the independence movement in what was then East Pakistan.

Defences again proved inadequate when another cyclone struck on April 29, 1991, with winds reaching 140mph during a high tide, producing a storm surge as much as seven metres high. More than 130,000 people were killed.

Cyclone disasters have always plagued Bangladesh. In 1876 one million people were believed killed in a storm and another million died from an outbreak of cholera afterwards.

But the problem is growing worse as rising sea levels, caused by global warming, increase the threat of storm surges and flooding. The delta region is also subsiding, partly because groundwater is being abstracted for agriculture.