Fresh rains in north India have flooded new areas and worsened the situation in regions already badly hit by some of the worst floods in 30 years.
Some people have seen their houses washed awy
Relief operations are being hampered in Bihar and Uttar Pradesh and landslides suspended the pilgrimage to a key shrine in Uttarakhand state.
In Bangladesh, more than 50,000 people have fallen sick after eating stale food or drinking contaminated water.
About 28m people have been affected by floods in India, Bangladesh and Nepal.
The number of those killed varies widely from 500 to 3,000.
In the worst affected Indian state of Bihar, officials say at least 300 people have died from the floods.
Rain water has destroyed crops worth millions of dollars and left hundreds of thousands homeless, they say.
Many in Bihar are complaining they still do not have enough supplies
Kanti Devi, a resident of Muzaffarpur, said: "The first time the flood water came in to my house it stayed for eight days. The water came back yesterday; almost 100 houses are flooded again here."
She has had to seek refuge elsewhere with her family.
"Everybody is nervous and scared. The children are frightened of snakes and leeches brought by the flood."
Children's NGO Plan says doctors report suspected malaria cases up 30-fold since the beginning of the floods.
Manish Mehta of Plan said: "If rain continues to fall, further assistance will be vital to prevent a disease epidemic, provide shelter and avert many more deaths."
In Himachal Pradesh state, where a flash flood caused by a cloudburst in Ghanvi village struck this week, two more bodies have been recovered from the debris of houses.
Eight people are confirmed dead and 44 are still missing, state officials told the BBC.
Officials say the relief work is being hampered as roads leading to the village have been severely damaged and it is difficult to move in heavy machinery.
THE ASIAN MONSOON
Monsoon winds blow north-easterly for one half of the year, and from the south-west for the other half
South-westerly winds bring the heavy rains from June to Sept
Winds arrive in southern India six weeks before the north west
Annual rainfall varies considerably
Incessant rains in several parts of Uttarakhand have killed 40 people and several highways have been blocked.
The pilgrimage to the Hindu shrine of Badrinath has been suspended after a 50-metre stretch of the national highway was washed away following heavy rains.
Rain has also battered the eastern city of Calcutta for a third day, disrupting transport and closing shops.
It has also continued to lash parts of eastern Uttar Pradesh and officials say the water level in major rivers, including the Ganges and Ghagra, has been rising steadily.
In Bangladesh, officials say nearly 500 people have died from the floods.
Doctors and health officials are struggling to cope with a major outbreak of disease which has put great pressure on the country's medical facilities.
At least 53,000 people have contracted water-borne diseases and officials say extra health workers have been deployed to treat those suffering from diarrhoea.
Many flood victims' homes are still under water.
"Now we have taken shelter beside this road," one victim, Zulekha Begum, told Reuters.
"I am with two of my young children suffering so much and no-one has come to help us as yet. In other places victims have been given aid, but we are not getting any," she said.