Bangladesh’s Prime Minister Sheikh Hasina said on Tuesday that the country’s flood has killed at least 100,000 people and left hundreds of thousands homeless.
The government has declared a state of emergency for two months to ensure the country does not suffer another such disaster.
“We are now going to be the world’s largest humanitarian crisis, and it is an enormous tragedy for Bangladesh,” she said.
A total of about 50 million people are expected to be affected by the floods, with some estimates of about half of the country living in extreme poverty.
About 5.7 million people have fled their homes, and tens of thousands are in shelters in towns, cities and villages, the World Food Programme (WFP) said on its website.
The UN refugee agency (UNHCR) warned that some of the worst affected areas are in the impoverished North East of the capital, Dhaka.
The region, which was hit hard by the monsoon rains in the early hours of Friday, is already suffering from flooding, with water levels in some neighbourhoods reaching six metres (20 feet) above the sea level.
Many homes in the region are submerged by water.
On Tuesday, Bangladeshi officials said the government had deployed 10,000 troops to the countrys north and east to protect the capital from floods and to fight fires.
But officials have also been urging people to stay indoors to help ease the effects of the drought.
Some cities have seen outbreaks of cholera, an infection that can lead to diarrhoea, and many more people have been forced to seek refuge in hospitals.
The World Food Program said its humanitarian response team has received about 20,000 cases of choriasis, which causes high fevers, in the past three days alone.
It has also said the number of cases of malnutrition and diarrhea has reached record highs.
Many people are still struggling to make ends meet, with food prices running at more than $200 a day.
The Bangladesh government said it would offer free fuel to people who have run out of money or are unable to afford food.
In neighbouring India, more than 5 million people were affected by flooding in parts of Uttar Pradesh state, leading to widespread food riots.
Authorities in both countries are also struggling to cope with a massive influx of refugees fleeing the violence.
India said it had received around 9.5 million refugees from the floods and neighbouring states, while neighbouring Nepal said it has welcomed more than 2.5 lakh refugees from Bangladesh and Pakistan.