(CNN) -- Thousands were left homeless Friday after a powerful tropical cyclone crashed ashore in Bangladesh, uprooting trees, destroying homes and damaging buildings where residents had sought shelter.
Selva Sinnadurai, head of the International Federation of the Red Cross delegation in Bangladesh, told CNN that power and telephone lines were also down, making it difficult to assess damage.
"Many are feared dead," Sinnadurai said.
CNN International meteorologists said that Sidr slammed ashore around 9:45 p.m. (1445 GMT) Thursday along the India-Bangladesh border as a Category 4 storm. Meteorologist Kevin Corriveau said the storm sped up as it approached shore and reached land before forecasters had predicted it would. As it crossed over land, it began to weaken but still brought torrential rainfall and floods to the low-lying area.
As the cyclone neared landfall Thursday night, volunteers were banging drums and trying to get people in low coastal areas in Bangladesh to evacuate, a spokeswoman for the Bangladesh Red Crescent Society said.
"About 600,000 people have already evacuated," Nabiha Chowdhury told CNN Thursday night. She put the total number of people in areas along the coast at about 2 million, but said it was difficult to tell because of the many tourists that flock to the region.
Sinnadurai said about 30,000 volunteers along Bangladesh's coast were taking people to cyclone shelters.
World Vision, the international aid agency, said Thursday it is working with volunteers to help house 20,000 people.
Bangladesh, low-lying and with isolated villages, is extremely susceptible to the storm surge Sidr is expected to bring. The Bangladesh Meteorological Department estimated Thursday that Sidr would cause a storm surge of 15 to 20 feet above normal tides for some lower coastal areas.
The Bangladeshi government was not allowing fishing boats or trawlers in the northern part of the bay to leave shelters "until further notice," the country's Web site reported.
In neighboring India the army remained on alert, army officials said, adding that all precautions had been put in place.
The U.S. Embassy in Delhi has issued a statement to Americans in the region, warning of "heavy rains, flooding, strong winds, damage to buildings, and other life-threatening conditions."
"Immediately prepare for the possibility that they could be without power and/or communications and unable to move by road for some time if the storm hits their area. Airports and seaports are also likely to be closed should the storm intensify as expected," the Tuesday statement says.
It appeared Bangladesh would bear the brunt of the storm, only months after monsoon rains brought misery across much of the country. The United Nations called the August flooding in India, Nepal and Bangladesh "the worst flooding in living memory."
And Bangladesh has a long history with deadly cyclones. In 1991, a devastating cyclone killed at least 140,000 people, according to the United Nations. And in 1970, Cyclone Bhola struck Bangladesh -- then East Pakistan -- killing 500,000 people. The U.S. National Oceanic and Atmospheric Administration considers that storm to be "the greatest tropical system disaster" of the century.
Aid officials hoped the country's experience with natural disasters would help people respond to Sidr.
"We hope the number of casualties would be at a minimum," Sinnadurai said. But the "damage to property" cannot be discounted, he said.
The humanitarian organization Save the Children had also prepared for "an impending emergency" in Bangladesh.
The organization's director there, Kelly Stevenson, noted the area's "very poor population." He said dry food, medicine and potable water would be in high demand after the storm subsides. E-mail to a friend