Millions of people are stranded by flooding in northeast India with concern growing about food and water supplies.

At least 5.8 million people have been displaced — a million more than on Monday — and some 30 have died in the past two weeks in the tea-growing state of Assam due to the monsoon rains, local government officials said.

Many thousands in the state are making do with only the most meagre food supplies and dirty water.

"We've just been surviving on boiled rice for almost seven days now," said Anamika Das, a mother at Amtola relief camp in Assam's Lakhimpur district.

She said she was having difficulty breastfeeding her baby boy.

At least 153 dead

Assam has been the worst-affected part of India. Floods have also hit neighbouring Nepal and Bangladesh.

At least 153 people have been killed in India, Nepal and Bangladesh. Parts of Pakistan have also seen flooding.

A woman displaced by the recent flood sleeps inside a classroom of Shree Sarsawati Higher Secondary School at Bhalohiya village in Rautahat, Nepal. (Riwaj Rai/Reuters)

Subhas Bania, also sheltering at Amtola, said authorities had made no provision for the supply of drinking water.

"We've been forced to drink muddy water," he said.

The rains in north India usually last from early June to October, with the worst of the flooding usually later in the season.

Assam is frequently swamped by floods when the Brahmaputra River, which flows down from the Himalayas through northeast India and Bangladesh, sweeps over its banks.

Water levels on the river and its major tributaries were beginning to fall, although they were still above the danger mark in places, the government said.

"We're trying our best to reach out to the affected people in whatever way possible, but yes, the situation is indeed very bad," said Assam Social Welfare Minister Pramila Rani Brahma.

'Where do we go from here?'

The government has yet to assess the impact of the floods that have battered thousands of settlements.

Bhabani Das, a village elder in Golaghat district, who has been living under a plastic sheet for four days, said the flood had swept away his home.

Villagers use a makeshift raft to cross a flooded area on the outskirts of Agartala, northeast India. (Jayanta Dey/Reuters)

"Where do we go from here?"

In the state of Bihar, which has also been hit by severe flooding, officials said floodwaters were beginning to recede after killing 33 people.

"Things are gradually becoming normal, people are returning home," Bihar Disaster Management Minister Lakshmeshwar Roy said.

Water levels in four rivers in Bangladesh, including the Brahmaputra, were above the danger mark, with some northern parts of the low-lying country flooded.

Road and railway links between the capital city Dhaka and at least 16 northern and northwest districts had been severed, officials said.