More than 1200 people have died across India, Bangladesh and Nepal after the worst monsoon floods to hit South Asia in more than a decade.

At least five people have been killed in India's financial capital Mumbai, as heavy monsoon rain caused transport chaos and forced schools and many offices to close on Wednesday.

The coastal city of more than 20 million people is the latest to be hit by floods that have ravaged South Asia this monsoon season, affecting millions of people.

"Five people have died in the Mumbai floods. Four of them, including two children, died due to wall collapse in the slums and another person died due to electric shock," Tanaji Kamble, a local government official, told AFP.

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Kamble said the rains had eased by Wednesday. "We are monitoring the safety situation across the city and things are returning to normal."

The carcass of a tiger lies in floodwaters in the northeastern Indian state of Assam. Photo / AP
The carcass of a tiger lies in floodwaters in the northeastern Indian state of Assam. Photo / AP

Cars were submerged and commuters waded through waist-deep water on Tuesday evening.

"I could not find any mode of transport and spent my night on the streets instead of trying to reach home," said 62-year-old Gangadin Gupta.

He said many people had been stranded for much of the night until the rail network reopened early on Wednesday.

India, Nepal and Bangladesh all suffer frequent flooding during the monsoon rains, which begin in June and last until September or October.

The United Nations said 41 million people in those three countries were affected by the floods.

The Red Cross says this year's floods are the worst for decades in some parts of the region.

It says entire communities have been cut off and many are short of food and clean water.

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The state of Bihar has been particularly hard hit. More than 500 people were killed this monsoon season.

About 1.7 million people were reportedly affected by the floods, which are now receding.

The tragedy in South Asia come as the world focuses on the impact of Hurricane Harvey in Texas.