Another 69 were injured when the structure came down around 2am (2030 GMT Monday) in a slum settlement, Tanaji Kamble, a disaster management spokesman for Mumbai’s local authority, told AFP.
The tragedy came as the teeming coastal settlement of 20 million residents was lashed by heavy rains for a second consecutive day, bringing the city to a virtual standstill.
Authorities declared Tuesday a public holiday and advised all residents to stay indoors. Schools and colleges were closed while flights were diverted from Mumbai’s main airport.
Large swathes of Mumbai received around 100 millimetres (4 inches) of rain overnight into Tuesday morning, leaving low-lying parts submerged in water.
Train services on Mumbai’s colonial-era rail network, a lifeline for the city’s population, were reduced due to waterlogged tracks while motorists were seen pushing cars through flooded streets.
Rescuers were sifting through the wreckage of the wall that collapsed in a slum area in Mumbai’s north, in the hope of finding more survivors trapped under rubble.
“Rescue operations are underway and more details are awaited. Besides, a team of fire brigade and local police also reached the spot and took control of the situation,” a National Disaster Response Force official told the Press Trust of India news agency.
Mumbai’s streets regularly flood during the monsoon, which runs from June until September or October, and which provides India with most of its annual rainfall.
In 2005, 950 millimetres (37 inches) of rain fell on the coastal metropolis in just 24 hours, killing more than 500 people.
In August 2017, intense rainfall brought the commercial hub to a virtual standstill for two days and left at least 10 people dead.
Building collapses are common during the monsoon when dilapidated structures buckle under the weight of continuous rain.
Activists say Mumbai’s susceptibility to floods has worsened in recent years due to a construction boom that is trying to keep up with the city’s swelling population.
Much of Mumbai’s mangrove cover, which is extremely effective in helping to drain water, has been destroyed over the past decade to make way for glitzy high-rises.
According to various studies, anywhere between 40 to 50 percent of the city’s population live in slums, which become a sea of blue tarpaulin every monsoon as residents try to keep out the rain.