Two toddlers are among more than 1200 people to die across India, Bangladesh and Nepal in the worst flooding to strike South Asia in years.

Floods caused by heavy monsoon rains destroyed homes and disrupted traffic in India's financial capital Mumbai, police said, while several villages in the east Indian state of Bihar were still inundated, with people living in makeshift shelters for days amid widespread heavy damage to farmland.

Police said a 45-year-old woman and a 1½-year-old child, members of the same family, died after their home in the northeastern suburb of Vikhroli crumbled on Tuesday, while a 2-year-old girl died in a wall collapse.

CATHAL MCNAUGHTON/REUTERS People wait to be rescued from a flooded village in the eastern state of Bihar, India.

In the neighbouring city of Thane, three people died after being swept away by floods, police added. Some died by falling into open manholes in flooded streets in various suburbs.

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Mumbai Police spokeswoman Rashmi Karandikar said seven other people were missing in Mumbai.

NAVESH CHITRAKAR/REUTERS A girl stands in front of a house at the flood affected area in Saptari District, Nepal.

In neighbouring suburbs six people were missing, said a police official, who declined to be named.

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.

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

NAVESH CHITRAKAR/REUTERS A boy walks along the flooded area in Saptari District, Nepal.

Several firms 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," the Mumbai Police tweeted. "Thank you all for showing what humanity is in the face of adversity!"

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

MOHAMMAD PONIR HOSSAIN/REUTERS Houses are seen flooded in Gaibandha, Bangladesh.

More heavy rains had been forecast for Wednesday (Thursday NZT), forcing the government to order schools and colleges shut, but in many areas the downpours were lighter.

The city and suburbs received a few showers in the last few hours but rainfall wasn't heavy like yesterday," said KS Hosalikar, a senior India Metrological Department official.

"However in the next few hours Mumbai and adjourning areas are likely to get fairly widespread rainfall, which will be heavy in few pockets."

Meanwhile local officials in Sierra Leone's capital, Freetown, said this week that the death toll from floods and mudslides triggered by intense overnight rainfall on August 14 had passed 1000.

The United Nations said that 41 million people in Nepal, India and Bangladesh were affected in one way or another by the floods.