|People have been forced to leave their homes in Ahmedabad, the largest city in Gujarat|
The United Nations estimates that at least 41 million people have been affected by the flooding in India, Bangladesh and Nepal.
In Bangladesh alone, the UN estimates that more than 640,500 homes have been destroyed, and authorities say at least 106,000 people are in emergency shelters as a result of the flood.
The monsoon rains have caused problems in northeast India, Bangladesh and Nepal
The director general of health services in the country said more than 13,000 cases of waterborne diseases have been linked to the flooding, including diarrhoea, skin diseases, acute respiratory infections and eye infections.
"People are going to be displaced, waterborne diseases are going to be a problem and food supply will be a problem," Mark Pierce, the country director for Save the Children in Bangladesh, told Sky News.
This year's monsoons have been much worse than usual
Some 9,000km of roads and 500 bridges have been damaged in Bangladesh, further complicating the relief effort.
In India, heavy rains brought Mumbai to a halt on Tuesday, closing train services, and a hospital was flooded as high tides threatened the city further.
Doctor Ashutosh Desai said staff were worried about infections among patients.
"The rain water is circulating rubbish that is now entering parts of the emergency ward," he said.
|The monsoon rains have caused problems in northeast India, Bangladesh and Nepal|
Government officials in the Indian state of Bihar said that at least 514 people had been killed by flooding there in the past few days.
Thousands have been sheltered in relief camps as a result and 17.1 million people have been affected in the state, prompting Prime Minister Modi to announce a relief package of $78 million.
Transport infrastructure has been badly damaged by the flooding
Monsoon rains, which tend to begin at India's southern tip and sweep upwards across four months, frequently result in high death tolls.
But this year has proved worse than usual.
The heavy rains come as Hurricane Harvey wreaks havoc across Texas , and follow disastrous flooding that killed hundreds in Sierra Leone.