Soldiers in motor boats rescued thousands of marooned people and helicopters air-dropped food as the number of people made homeless after some of the worst flooding in years in India's northeast rose to 3.5 million.

About 10 million people out of the 27 million population of Assam state have been affected by flooding after rains in the past few days. More than 2,000 villages have been completely submerged.

The second spell of flooding in less than a month has also spread across parts of Bangladesh.

Around half a million were left marooned in their swamped villages on Tuesday after water was released from the flooded reservoir of a hydroelectric plant.

A dam official said the water was released from the reservoir to protect the plant. Hundreds of homes, huge areas of crops and infrastructure have been damaged.

In India's Assam, about 3 million people are living in temporary shelters, government buildings and schools, officials said.

"The situation is grim," the chief minister of the tea- and oil-rich state, Tarun Gogoi, told Reuters on Tuesday.

Around 400,000 ha (one million acres) of farmland have been flooded.

Since the annual monsoon rains began in June, about 50 people have been killed in Assam.

In the neighboring state of Manipur, at least 55,000 people have been rendered homeless and are staying in more than 30 relief camps.

Road links to the tiny state of Sikkim, which borders China, remained disrupted as a large stretch of the main highway connecting the state with rest of the country was blocked by landslides.

The regional weather office in Guwahati -- the main city in the country's northeast -- forecast more rains in the next 48 hours.

Prices of essential commodities have shot up across the region as landslides and flooding blocked highways at many places and trucks carrying food and medicines were stranded.

The chief minister of Manipur, Okram Ibobi Singh, ordered officials to release government food supplies for victims.

In Bangladesh, where about 850 people have died since late July, another 10 died overnight. Around 1.5 million are homeless or marooned, officials said.

Officials said the latest floods had started to ebb slightly in the country's north.

(Additional reporting by Azad Majumder and Ruma Paul in Dhaka)