By Alistair Lawson BBC correspondent in Dhaka

The Bangladesh authorities say water levels in all the country's rivers are rising, and have warned relief workers to stay on the highest alert.

At least 12 people have been killed in flood-related incidents following heavy monsoon rains over the last few days.

Major rivers, including the Brahmaputra and the Meghna, may burst their banks soon as water from neighbouring India runs through the country. Large areas of Bangladesh have already been inundated by heavy rain, leaving thousands of people marooned or displaced.

Flood information centre officials are forecasting medium- to high-intensity floods.

They say conditions could get a lot worse over the next 10 days, as flood water enters the country from India.

Most of Bangladesh's rivers originate from the Himalayas and flow through India before reaching the Bay of Bengal.

1998 floods

The Bangladesh flood information centre says that while the situation is not yet a crisis, matters will take a marked turn for the worse if the current high levels of rainfall continue.

Five million are not getting aid and drinking water

Many people have drawn comparisons between the unusually heavy rainfall at the beginning of July and the last big floods of 1998, when hundreds of people were killed.

All the country's main rivers are rising, including the Brahmaputra, which officials say is now in danger of breaking its banks in numerous places.

The fear now is that two other large rivers, the Ganges and the Meghna, may also break their banks.

If that happens, Bangladesh will once again be facing a large natural disaster.

Homeless

In the northern district of Kurigram 300 families were made homeless because of floods made worse due to river erosion.

Some families have been forced to take refuge on the roofs of houses or government buildings.

With the danger of crops being lost the authorities say that they are now making efforts to supply food and other essential items to flood victims.

They say that they are concerned about outbreaks of water-borne diseases, such as diarrhoea, once the water starts to recede.