At least 173 people have died and millions more have been displaced across northern India, southern Nepal and Bangladesh after heavy monsoon rains unleashed landslides and floods.
Officials are still trying to determine the scale of the disaster, as weather forecasters predicted more rain for some areas and casualties were reported in multiple locations across the Himalayan foothills of South Asia.
Nepalese police are searching for scores of people reported missing after rivers burst their banks and killed at least 80, according to police.
Many of those killed had drowned or been caught in collapsed houses or crushed underneath toppled trees.
The floods destroyed key rice crops in Nepal and drove thousands of farmers and their families to take refuge in schools or tents on higher ground, as water submerged roads and cut transport to affected areas.
Near the Nepalese village of Kunauli, on the border with India, people were sheltering in tents pitched along the main highway after the land on both sides became inundated.
Electricity and mobile phone services were cut off. Soldiers passed out clean water, grain and rice, which people were cooking on small, paraffin-fuelled stoves.
However, aid workers said some did not have enough food or water.
"The heavy rains hit at one of the worst times, shortly after farmers planted their rice crop," Sumnima Shrestha, a spokeswoman for the US-based anti-poverty charity Heifer International, said.
"Making matters worse, large numbers of livestock have been swept away in the flash flooding."
Across Nepal's southern border, flooding swamped seven districts in the Indian state of Bihar and left more than half a million people homeless.
Officials said two people had also died.
Landslides and flooding are common across South Asia during the summer monsoon season, and have become more dangerous thanks to widespread deforestation and poor urban planning which makes it harder for the land to absorb rainfall.
Bangladesh was bracing for worse flooding on Monday, as weather forecasters predicted more rain.
At least 18 major rivers are flowing at dangerously high levels, according to the state-run Flood Forecasting and Warning Centre.
Twenty-seven people have been killed over the last few days in the low-lying delta nation, while another 600,000 are marooned, according to Bangladesh's disaster management minister, Mofazzal Hossain Chowdhury.
Around 368,000 people have taken refuge in more than 970 makeshift government shelters, he said.
Bangladeshi soldiers were working to evacuate those who were stranded on rooftops or in trees, after floodwaters inundated hundreds of northern villages.
In the north-eastern Indian state of Assam, the floodwaters have damaged bridges, downed power lines and washed away thousands of homes.
Officials said that at least 2.5 million people had been affected, including some 200,000 now staying in 440 relief camps, and that 18 people had been killed.
With railway lines inundated, the remote region was largely cut off from the rest of the country.
Indian air force helicopters are dropping food and drinking water packets in the worst-hit districts, said Assam's chief secretary, VK Pipersenia.
Indian prime minister Narendra Modi said he was in contact with Assam's authorities.
He said on Twitter: "All possible support is being provided to Assam for overcoming the flood situation prevailing in parts of the state."
Most of Assam's Kaziranga National Park was also underwater, forcing many of the wildlife reserve's endangered rhinos and deer to move to higher ground.
Dozens of deer were killed by cars after they leaped onto a nearby highway to escape the floods.
Farther to the west, in the Indian state of Himachal Pradesh, soldiers recovered the bodies of 46 people who had been travelling in two buses buried in a massive landslide of rocks and mud on Sunday.