By Roland Buerk BBC correspondent in Dhaka

Water in Dhaka is getting dirtier with untreated sewage

Rivers are now receding in the north and north-east, but at least 40% of the capital, Dhaka, remains flooded.

The disaster response experts are in Bangladesh to assess what is needed.

Bangladesh's government has estimated the damage to roads, bridges, schools and hospitals at $7bn. At least 30m people remain homeless or stranded.

ASIAN MONSOON The word 'monsoon' comes from the Arabic for 'season' Describes seasonal reversals of wind direction From April heat builds over South Asia, creating low pressure areas Brings moisture-rich south-west winds in from the ocean Why floods are so bad BBC Weather: Asian monsoon

Forecasters say they expect the rivers in the north and north-east of Bangladesh to continue to recede.

The UN is preparing to appeal to member countries for more money to help distribute food and medicine and to rebuild infrastructure once the waters subside.

Aid agencies working here say the country has sufficient emergency supplies of food, but the difficulty is getting it to areas cut off by the flooding.

But as the waters go down, outbreaks of diarrhoea are increasing.

In central areas around the capital, there will be no let-up in the flooding for at least another 48 hours.