Relief workers were struggling today to get essential food and medicines to hundreds of thousands of survivors after a cyclone devastated a huge swathe of Bangladesh killing more than 500 people.

Most of the deaths during the storm, which had wind speeds of 150mph (240kph), occurred when trees fell on flimsy bamboo and tin-built houses. Police said that the death toll and the number of casualties would rise.

Sixteen-foot waves washed away hundreds of thatched homes, destroying crops and killing livestock. Television news reports said that more than a hundred fishing boats in the Bay of Bengal had failed to return home overnight. Many small boats were without radio equipment and may not have heard the storm warnings.

Electricity poles were uprooted, disrupting communication and power supplies. Evacuees sheltered in schools. “We have been virtually blacked out all over the country,” said a disaster management official in southern Mongla, one of the worst-affected areas.

Teams of rescuers were deployed to conduct relief operations in the worst-hit areas in the country’s southwest but relief work was hampered because power and phones were down in many areas. Thousands of people had been left homeless.

Mollik Tariqur Rahman, a local businessman in the affected area, said that 80 per cent of the homes in his village had been flattened.

“I cannot describe how devastating it was. It was like doomsday, the most frightening five hours of my life. I thought I would never see my family again,” he said.

A navy spokesman said five ships had been dispatched with supplies of food, medicine and relief materials.

The European Commission said it was releasing 1.5 million euros in emergency relief aid to the country.

“Preliminary indications are that the most pressing needs will be food, safe drinking water, emergency shelter, clothing, blankets and medicine,” John Clancy, Commission spokesman, said.

The Bangladeshi meteorological department described cyclone Sidr as similar in strength to the devastating 1991 storm that triggered a tidal wave killing 138,000 people.

But it said that the latest storm had weakened overnight and was progressing through the northeastern state of Sylhet. Sidr is expected to fizzle out over the northeastern Indian state of Assam tomorrow. “It has lost its intensity,” a weather forecaster said.

Officials in one of the world’s poorest nations, with a population of 140 million, were spared more serious human casualties because of an early warning system and network of cyclone shelters introduced after the 1991 disaster.

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 a third of Bangladesh lies less than six metres above sea level.

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 (3,000 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 a 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.

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