Hundreds of people have died and millions have been left homeless across South Asia since the start of the annual monsoon season in mid-June.
Below are details of the worst-affected areas and the aid effort that has been mobilised to help the estimated 20 million people coping with some of the worst monsoon flooding in living memory.
More than 12 million people have been stranded or left homeless in the northern states of Bihar, Uttar Pradesh and Assam.
About 80 people have been swept away by flooded rivers in these states, and more than 1,000 others killed in other flood-related incidents in India over the last three weeks.
Recent heavy monsoon rains have flooded villages in the western state of Gujarat.
In the worst-affected areas, some villages have been submerged beneath 6ft (1.8m) of water.
The army and air force have joined relief operations but victims, complaining of inadequate food supplies, have clashed with police in several relief camps in Assam, where the situation is worst.
The main road connecting India's seven north-eastern states to the mainland through Assam is flooded in several places and more than 60 bridges have collapsed.
About five million people have been displaced or marooned by the flooding, according to government figures, and 64 people have been killed.
Some two-thirds of the country is believed to be underwater.
Thousands of families have taken shelter on higher ground, taking the tin walls and roofs of their houses with them to ensure they can rebuild their homes when the water eventually recedes.
The government insists it can cope, but the relief effort is patchy.
As the monsoon rains from Nepal and north-east India work their way into the Bangladeshi river delta, flood levels could rise further.
A prolonged crisis would leave hundreds of thousands at risk from hunger and disease, correspondents say.
More than 250,000 people have been affected by the torrential rains.
There have been deadly landslides in the highlands and floods have hit dozens of districts in the low-lying Terai region - the country's most heavily populated area.
The weather is improving, but aid workers say that the problems for many of the affected people are getting worse.
Food stocks are running low, polluted water means there is an ever-greater risk of disease and there is a growing fear that crops could be permanently damaged.
Aid efforts, led by governments, international agencies and non-governmental organisations, are focusing on the immediate needs of those who have lost their homes - water and sanitation, temporary shelter and food.
Across India, more than 180 relief camps and 155 temporary shelters have been set up by Unicef.
In the state of Uttar Pradesh alone, the Indian government says it has set up 820 relief camps, housing almost 600,000 people.
In Nepal, the World Food Programme is sending three months of emergency rations to 60,000 of the flood victims.
Aid agencies are distributing plastic sheeting, blankets, water buckets, oral rehydration salts and water purification tablets.
Boats are being used to deliver supplies but some areas are accessible only by air, making relief efforts challenging.
As floodwaters recede, the aid effort has shifted to preventing outbreaks of waterborne diseases such as diarrhoea and malaria.
The longer-term relief efforts will focus on rehabilitating waterlogged fields and crops and repairing damaged schools and vital infrastructure.