There is an urgent need for rescue and relief services on the Indian subcontinent as severe monsoon flooding spreads across India, Nepal and Bangladesh, leaving more than 1,200 people dead since the rains started.

Key points: UN says 40 million people affected

UN says 40 million people affected Building collapses in Mumbai as city floods

Building collapses in Mumbai as city floods Worst flooding in some parts of Bangladesh in nearly 30 years

Oxfam said its Bangladesh staff reported two-thirds of the country was under water and in some areas the flooding was the worst since 1988, creating an urgent demand for humanitarian supplies.

Widescale flooding in an arc stretching across the Himalayan foothills caused landslides and washed away tens of thousands of homes and vast swathes of farmland.

The UN said about 40 million had been affected.

Oxfam says two-thirds of Bangladesh is under water. ( Reuters: Mohammad Ponir Hossain )

Two toddlers were among 14 of the latest deaths as heavy rain destroyed homes and disrupted traffic in India's financial capital, Mumbai.

Several villages in the east Indian state of Bihar are still inundated, with people living in makeshift shelters for days amid widespread heavy damage to farmland.

The deluge in Mumbai — nearly a month's average rainfall in a single day — halted train services and led to flight cancellations.

A building collapse in the city left 12 people dead and at least 25 others trapped.

Forecasts of more heavy rains forced the Government to order schools and colleges to shut.

A baby is rescued from a flooded village in the eastern state of Bihar. ( Reuters: Cathal McNaughton )

School children wade through a waterlogged street in Mumbai, India. ( AP: Rajanish Kakade )

"Mumbai and adjoining areas are likely to get fairly widespread rainfall, which will be heavy in a few pockets," KS Hosalikar, a senior India Metrological Department official, said.

Officials said train and air services were operating normally late on Wednesday in Mumbai, home to India's two biggest stock exchanges and several major companies.

The deluge revived memories of 2005 floods that killed more than 500 people, the majority of them in shantytown slums where more than half of the city's 20 million people live.

Many parts of Mumbai are under water following heavy rain. ( Reuters: Danish Siddiqui )

Unabated construction on floodplains and coastal areas, as well as stormwater drains and waterways clogged by garbage made the city increasingly vulnerable to storms.

Several companies made arrangements to provide food and rest areas for employees stuck in offices, while officials of temples and religious bodies offered help to those stranded on streets.

"Together, we can overcome any ordeal," Mumbai Police tweeted.

"Thank you all for showing what humanity is in the face of adversity!"