Hundreds of thousands stranded on rooftops in rising India floodwater

More than a week of torrential rainfall has forced people from homes and cut off access to food and clean water

Villagers take shelter on the top of their homes in Morigaon district of Assam state on Monday amid widespread flooding in north-east India. AFP

Flood waters rose on Monday across north-eastern India where hundreds of thousands of people are stranded on the roofs of their homes or have fled to higher ground as more torrential rain fell.

Incessant downpours for more than a week caused the Brahmaputra and other major rivers to burst their banks across Assam and Bihar states.

Many villages are submerged by up to two metres of water. Experts say annual floods which hit the region are getting worse because of climate change.

At one dam, authorities released water fearing the walls would collapse.

The floods threatened to deluge a Unesco World Heritage-listed reserve that is home to the world's largest concentration of one-horned rhinos.

Tens of thousands of people are stuck in villages cut off by the floods and the state governments said more than 400,000 had been moved to higher ground.

Anuwara Khatun, 16, said she and her family had spent nearly a week on the roof of their home in Assam's Morigaon district.

"The water level has been rising for five days now," she told AFP from the village of Ghasbari on the banks of the Brahmaputra.

"A lot of families are stuck on their roofs. There is a shortage of essential supplies so we only eat once a day. There is no hygiene here."

Santosh Mandal moved his family to a sandbank in Bihar's Supaul district after his village was flooded.

"There is no clean water to drink, food to eat and the children are crying for milk. We are praying for help because the government has yet to send relief," he said.

The Bihar government has sent rescue boats to move people to safety but these are concentrated in the worst-hit districts.

The Bihar and Assam governments said more than 12,000 people were in relief camps.

The Bihar government opened up the Valmiki Gandak dam, warning people in nearby villages to move away, after 16 centimetres of rain fell in 24 hours.

About 70 per cent of the 430-square-kilometre Kaziranga National Park in Assam is underwater, putting the lives of its rare one-horned rhinoceroses, as well as elephants and wild boar, at risk.

Himanta Biswa Sarma, Assam's chief minister, on Monday made an urgent appeal for traffic to avoid an important road through the reserve.

He said animals that were seeking shelter on the road were now at risk.