"We have not been able to collect information about casualties in many remote and impassable places due to the disruption to communications."
In one village, residents told the AFP news agency that more than 100 people died when the area was engulfed by a tidal surge pulled in by the storm.
"A six-metre wall of water wrecked the village of Charkhali and 30 more people are still missing," said KM Abdul Wadud, a local government official.
Owen Fay, Al Jazeera's correspondent in Bangladesh, said that he witnessed worsening conditions as he travelled from the capital Dhaka to the coastal town of Barisal.
"As we get further and further away from the capital Dhaka and closer the coastal regions ... the devastation gets worse," he said.
Fay said: "We have seen homes and livelihoods completely destroyed.
"The government is seeing the scale of the storm for the first time and although they say they have a plan in place, they did not realise how badly some of these places have been hit."
Residents in southern districts near the coast bore the full brunt of the storm and told of their terror as they were hit by wind speeds of up to 240kph.
Fulmala Begum, 40, said she was not warned to evacuate and had to take refuge under a bed with her husband and two children as the storm roared around her.
"Five hours later we found ourselves under a heap of tin roofs and two huge trees. Not a single house in my village was spared the catastrophe," she said. 'Great human tragedy'
A district official said Bangladesh suffered another "great human tragedy".
He said that in Jhalokati district, 140 km south of the capital Dhaka, every one of its 554 villages had been hit.
|The UN and the European Commission have|
pledged emergency aid to Bangladesh [AFP]
Experts describe Sidr as similar in strength to the 1991 storm that triggered a tidal wave, killing an estimated at least 140,000 people.
Another cyclone in 1970 killed up to half a million people.
But officials remained optimistic that this time the death toll - while still high - would reach the death tolls in previous disasters because of a network of cyclone shelters and an early-warning and evacuation system.
The UN has pledged several millions of dollars in aid while the European Commission said it is sending $2.2m in emergency relief to Bangladesh.