An estimated 40 million people in South Asia are struggling to rebuild their lives after massive floods devastated the region nearly a month ago.

Key points: Entire villages across Bangladesh, India and Nepal remain submerged since the floods began in mid-August

Entire villages across Bangladesh, India and Nepal remain submerged since the floods began in mid-August In Bangladesh, more than 8 million people were affected

In Bangladesh, more than 8 million people were affected The floods were so extensive, many families struggled to give the dead a proper burial because of the lack of dry land

Entire villages across Bangladesh, India and Nepal remained submerged under water since the floods began in mid-August.

Authorities have described it as the region's worst flood in 40 years, with a metre of rain falling in some areas in the space of days.

The worst-hit areas include Assam, Bihar and Uttar Pradesh states in northern India, the Terai region in southern Nepal, and Kurigram and Chimari districts in northern Bangladesh.

In India alone, UNICEF estimated 31 million people were affected by the floods, losing their homes, livelihoods, cattle or property.

In Bangladesh, more than 8 million people were affected, including about 3 million children.

Children, who tend to play in muddy waters, are particularly susceptible to waterborne diseases. ( Supplied: UNICEF/Narendra Shrestha )

And in Nepal, the number affected was about 1.7 million people.

At least 1.5 million homes are believed to have been destroyed or damaged, along with thousands of schools, hospitals, roads and bridges.

Of the 1,300 people killed, aid agencies said 30 to 40 per cent were children.

In Nepal alone, at least 160 people are dead and 25 missing.

The flimsy nature of many homes made them particularly vulnerable.

"The people are very poor here and houses are made of mud. So when floods came it washed away their houses, and in some places the water came so quickly, with such force, that one village I saw looked like [it was] hit by a tornado or cyclone," Rowkan Khan from UNICEF's office in Kathmandu said.

Villagers in Nepal struggle to find a piece of dry land. ( Supplied: UNICEF/Lilu KC )

Burials impossible without dry land

Indeed, the floods were so extensive, many families struggled to give the dead a proper burial because of the lack of dry land.

In Nepal, one family who lost their young son Kamal instead had to let go of his body to the floodwaters, and, grief-stricken, watched as the Koshi River swept him downstream.

Local media said the boy died from an illness, exacerbated by continuous exposure to rainfall and flooding at his remote village.

Even as the waters slowly recede, the danger of mosquito and waterborne diseases has risen, with children again bearing the brunt of the threat.

Health workers fear the worst could yet be to come.

"This is always the curious phenomenon, that waterborne diseases appear more," Ray Kancharla, from India's branch of Save the Children, said.

"This year, mosquito breeding is huge and already there have been dengue and malaria and chikungunya virus etc.

A baby suffering from dehydration cries after being rescued from a flooded village in the eastern state of Bihar, India. ( Reuters: Cathal McNaughton )

"So these risks are huge, especially for children and women. Children play in muddy waters so the skin infections also appear hugely."

In India alone, the agency said 17 million children were in urgent need of humanitarian assistance, including basic nutrition support, health care and education.

Tens of thousands of schools were also inundated or damaged, making it impossible for children to continue their education.

Save the Children's chief executive in India, Thomas Chandy, said it was heartbreaking to hear so many tragic stories of destroyed lives and homes.

"Some communities have been totally wiped out, with not a building left undamaged," he said.

"Many older people I met recounted the horror of the floods, which hit them out of the blue.

"They haven't seen anything like this in many years."

People's homes in Kurigram district in Bangladesh have been inundated by the floods. ( Supplied: Save The Children/Abdullah Seru )

Farmers too were counting the cost, with much of the affected area rural or farm land.

About 2.4 million hectares of cropland was lost to the floods.

Many farmers watched cattle and other livestock die or be swept away.

UN agencies, the Red Cross and other NGOs stepped up efforts to respond to the demand for food, medicine, clean water and water-purification tablets.

Mr Kancharla said many of those affected were hoping to be able to return to their homes — what is left of them — within a couple of weeks, as the water level continued to drop.

But he said it would be well into next year before they could return to normal life.

"The recovery is something we have seen takes a long time, to collect the debris, and clean up and rebuild their houses," Mr Kancharla said.

"Our guess is it will take a minimum six months to a year that they are able to restore their lives. And restoring their livelihoods will take a long time."