"Some parts of the district have got cut off in such a way with roads submerged that the people there cannot be reached by boats," said Manoj Srivastava, Bihar's disaster management co-ordinator.
Srivastava said 11.5 million people in Bihar were affected by the flooding and 6,000 villages were submerged.
"The data shows in Bihar in several districts the rainfall has been 250 to 300 per cent higher than the average for the last 30 years," he said.
|Air force helicopters have been dropping dry|
rations over flood-hit areas of Bihar [AFP]
He said that flood waters were beginning to recede.
However, a boat carrying up to 100 people overturned in the rain-swollen Ganges late on Monday, an official said.
"So far only one body has been found, 11 people swam to safety," Shravan Kumar, local administrator of Samastipur district, 150km north of state capital Patna, said.
"The remaining people seem to have been carried away by the very strong currents of the river."
Rivers were still overflowing in neighbouring Nepal, according to a UN official.
"If there is more water from Nepal then the situation will only get worse," Job Zachariah, the head of the Bihar chapter of Unicef, the child welfare agency, said.
"If there is more water from Nepal then the situation will only get worse"
Job Zachariah, head of the Bihar chapter of Unicef
Bihar's chief minister has blamed Nepal for the flooding, with officials saying that Kathmandu should build more dams to control the flow of waters south.
Nepal's foreign ministry said overflowing Indian dams on the border have flooded the Himalayan country's low-lying regions.
Health experts have warned that there could be outbreaks of water-borne diseases.
AK Pande, head of the Patna Medical College and Hospital in Bihar, said: "Receding floodwaters leave behind sludge and debris which become the breeding ground for epidemics."
Monsoon storms combined with melting Himalayan snow precipitated massive floods in late July from Nepal through northern India and Bangladesh.
The monsoon toll in Bangladesh, a delta nation prone to floods, stands at 282, more than half of whom died in the last 10 days, officials in the capital Dhaka said.
About nine million have been displaced.
Higher than normal
Owen Fay, Al Jazeera's correspondent in Bangladesh, says the level of flooding in the country is much higher than normal.
"In a normal season, about 15 per cent of the country suffers from moderate to severe flooding - this year it’s 60 per cent," he says.
|Flooding has seriously affected up to 60 |
per cent of Bangladesh's territory [AFP]
"As is usual, the most vulnerable are suffering the worst.
Alongside the risk of disease are the complications arising from malnutrition and dehydration."
Fakhruddin Ahmed, leader of the country's interim government, called for help during a live televised address late Sunday.
"I am making an appeal to people from all walks of life, irrespective of class and profession, to come forward spontaneously to the aid of the flood-affected," he said.
Canada has pledged $950,000 in emergency aid relief for flood victims.
"Canada stands with these countries as they carry out their relief efforts," Peter MacKay, foreign minister, said.