Severe flooding has hit the states of Bihar, West Bengal and Assam in north-eastern India and parts of Nepal while inundating more than one-third of Bangladesh.
The floods have been called the worst in the region in a century.
The immediate casualty figures have risen to over 700, but that figure is expected to grow, with millions more cut off or displaced.
In the streets of Bihar, in north-east India, rescue teams paddle through what used to be the street.
Hundreds of families seek refuge from the waters on the roofs of their galvanised-iron shacks, others wading through the destruction to find any belongings that can be salvaged.
Millions have lost their homes, and at least 500 in the province have lost their lives.
This man, named Ram, lost his teenage son Rohit when the boy was swept away in floodwaters last Friday.
"This has been the worst flood that we saw. It has taken lives and caused great loss. Our loss can never be compensated by anything. The one who was our only support is no more."
Several areas in north-east India remain cut off, with the floods destroying crops and roads and disrupting power supplies.
The district magistrate of Motihari in Bihar, Raman Kumar, says authorities are struggling to reach everyone.
"We are trying hard to reach them, but it may be possible that, some of the areas, we may not be reaching there. But especially for those areas, we are using boats and helicopters. In the last two or three days, we have done thousands of food packets."
An estimated 24 million people have been affected across India, Bangladesh and Nepal.
In Bangladesh, at least 115 people have died, with more than 5.7 million affected.
But aid agencies say they fear the worst is yet to come, with contaminated floodwaters posing the risks of cholera and dengue-fever outbreaks.
An International Federation of Red Cross representative in Dhaka, Azmat Ulla, says history shows disease inevitably comes as the floodwaters recede.
"While we're looking at the emergency response right now, we are also looking at how to deal with the recovery when it comes."
The military in Bangladesh is lining flood-affected areas with sandbags, with more destruction expected once the waters begin to flow down from the north.
Azmat Ulla says the emergency services are struggling to cope with limited supplies.
"Dried food, cooked food, emergency safe-drinking water, emergency shelter, helping to evacuate people and providing first aid."
In Nepal, over 140 people are confirmed dead, and 38,000 households have been displaced by flash floods and landslides.
Survivors are in desperate need of water purifiers and mosquito nets, and many claim the government has been slow to respond.
Meanwhile, some of the region's endangered animal species are also on the casualty list.
The floodwaters have been pouring into the Kaziranga national park in India's Assam state, killing over 200 animals, including 15 rhinoceroses and a Bengal tiger.
