Aid workers are struggling to reach hundreds of thousands of survivors from a powerful cyclone that ripped through southern and central Bangladesh.

At least 667 people are reported to have died during the storm, a toll that is expected to rise.

The cyclone has destroyed or damaged tens of thousands of homes.

But access to some of the worst affected areas is difficult with roads blocked by debris and power and phone lines cut.

With a huge relief operation now under way, the true extent of the destruction is expected to become clearer on Saturday, the BBC's Mark Dummett in Dhaka reports.

Military helicopters and ships joined the rescue efforts on Saturday, helping deliver supplies and medical assistance to some of the most remote areas.

The ships were also at work clearing channels blocked with sunken vessels.

On land, elephants were employed to clear some of the heavier debris from roads.

The storm hit Bangladesh late on Thursday, with winds rising to 240km/h (150mph).

It passed through the capital Dhaka hours later, before dying down in the north-east of the country.

'Trail of destruction'

Many villages have been leveled and the recent crop harvest has also probably been destroyed, correspondents say.

The biggest challenge for southern Bangladesh will now be reconstruction, the BBC's Mark Dummett says.

One witness in the south-western Bagerhat district told the news agency AFP that the storm had destroyed 80% of the homes in his village.

"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," said local businessman Mollik Tariqur Rahman.

"There is a trail of destruction everywhere. We can't even detect exactly where our houses were built - only a few are left and they do not have roofs," he said.

Many people are thought to have been killed as falling trees leveled fragile houses made of thatch, wood and tin.

The storm triggered 5m (16ft) tidal surges in many of the affected districts. Rivers flowing into the Bay of Bengal were said to be swollen and rising.

Death toll rising

At least 150 fishing boats in the Bay of Bengal have failed to return to shore.

Hundreds of fishermen are feared missing.

The United News of Bangladesh news agency said its tally, reached by adding up figures from its reporters across the country, came to at least 1,100, but this could not be verified.

Amid a virtual national blackout, the authorities have been struggling to get food, medicine, tents and blankets to the affected areas.

An official from the UN World Food Program said the most urgent needs were food, water purification tablets, and medicines.

The WFP is sending energy biscuits for 400,000 people. The government, the Red Crescent and other NGOs are also sending teams.

Bangladesh developed a network of cyclone shelters and a storm early-warning system, after a cyclone killed more than 500,000 people in 1970.

Casualties from cyclones have been significantly reduced as a result, officials say.

Southern Bangladesh is hit every year by cyclones and floods, but Cyclone Sidr is the most destructive storm to hit the country in more than a decade.

Another storm in 1991 left some 143,000 dead.

PHOTO CAPTION

An elephant pushes a stranded bus in Barisal, 16 November 2007