Over 1,000 people were feared killed and thousands of others went missing in Bangladesh as one of the deadliest cyclones battered the country's south-western coast, flattening houses and disrupting power supply plunging almost the entire country into darkness.

The government officials put the toll to over 260 and said it was likely to rise sharply.

Unofficial reports said the toll could be more than 1,000. The worst affected district is Barguna where unofficial sources said at least 450 people were killed.

At a press conference, Disaster Management Secretary Ayub Mian said, "There are remote areas and offshore islands where rescuers could not reach yet." He said the Barguna toll was yet to be confirmed.

At least 500 trawlers with over 3,000 fishermen have been missing since cyclone Sidr, packing winds upto 240 km, made landfall at Khulna-Barisal coast on Thursday evening and swept central Bangladesh, including the capital Dhaka.

Almost the entire country plunged into darkness with the collapse of the national grid. Power department officials said they could restore power supply in only 10 per cent of the areas.

They are expecting to restore the normal power supply within the next two days.

The power failure affected the transport system, water supply and telephone operations.

The army backed by air force choppers was called in to help in rescue efforts.

Other areas devastated in the cyclone included Dublar Char and districts of Khulna and Barisal.

Thousands of acres of paddy fields were damaged with lowlands being flooded in Patuakhali district, where 43 people died, officials said.

Nearly 80 per cent of shanties and thatched houses in coastal areas were destroyed, officials said.

Southern districts were plunged into darkness on Thursday evening itself after power was snapped. Gusty winds uprooted trees, electric polls and roadside billboards as the cyclone swept the country, including Dhaka.

Tidal surges of 15-20 feet inundated the low-lying areas, including Dublar Char, Nijhum Dwip, St Martin's Island, Shah Pori Char, Kochikhali and Kotka, in the coastal districts.

Over 6 lakh people, especially those living in the coastal zone, were evacuated in the last two days.

Airport and port operations remain virtually suspended.

The government had earlier announced red alert in the coastal zone. Chief Adviser Fakhruddin Ahmed and other officials were touring affected districts, officials said.

Met Office Director Samarendra Karmakar had earlier told reporters the cyclone was "strong like those in 1970 and 1991 and though there was a lot of time for preparations, minimising loss of property will not be possible."

Nearly 10 million people live in the coastal zone face the brunt of frequent cyclones in the country.

World Food Programme said it had deployed response teams in south-west Bangladesh to strengthen its local management. The WFP has created an operational alliance with 38 NGOs, including other UN agencies.