The BBC's Frances Harrison: "The forecast is for things to get worse"

Another half a million people are thought to be stranded as floods have engulfed new areas in the centre and north of the country.

More rain is expected

The Flood Forecasting and Warning Centre in Bangladesh said the three main rivers - the Brahmaputra, Ganges and Meghna - were still spilling over their banks.

Forecast officials warn there may be worse to come in many regions.

"We are expecting heavier rain over the next few days when the flooding could take an alarming turn," an official of the Bangladeshi meteorological office warned.

Officials say that central and southern areas are the most vulnerable, but the floods could also submerge vast areas around the capital, Dhaka.

Rooftops are used as shelters in low-lying areas of Dhaka

People in remote village are suffering from an acute shortage of drinking water and dry food.

The BBC correspondent in Dhaka says that in some areas, people have been getting respiratory infections.

According to newspaper reports there have also been outbreaks of diarrhoea and other diseases.

Rescue workers say the situation will get worse if clean sanitation and water is not quickly provided.

The government said it was doing everything possible to reach the stricken area with relief supplies to prevent an epidemic of water-borne diseases.