The death toll from monsoon flooding in eastern India climbed to 26 on Friday, with hundreds of villages cut off and an estimated four million people displaced, officials said.

Bridges were washed away and roads and railway tracks submerged by the swirling waters in West and East Midnapore districts, said West Bengal state's finance minister Asim Dasgupta.

"Telephone lines were snapped and electric poles uprooted. Nearly 2.5 million people were forced from their homes by flood in over 300 villages during the past four days," Dasgupta said.

"The death toll has risen to 26 as 15 people drowned during the past 24 hours," he said.

Helicopters were airdropping food and essentials as army personnel and aid workers struggled to reach the growing number of people marooned, he said, adding there also appeared to be no let-up in the heavy rains.

Defence spokesman R K Das said thousands of people were taking shelter on rooftops and elevated areas but were running short of food and drinking water.

In neighbouring Orissa, nearly a million people were cut off in the neighbouring eastern coastal state of Orissa, disaster management minister Manmohan Samal said earlier this week.

Further to the northeast, in Assam state, more than 350,000 people had taken shelter in government camps to escape from rising waters, the government said earlier this week, before flood waters started receding Wednesday.

Every year the monsoon causes the Brahmaputra river to flood, submerging paddy fields, washing away villages, drowning livestock and killing people in Assam, a remote state of 26 million people.

In 2004, at least 200 people died and more than 12 million were displaced in the floods.