MUMBAI: At least 21 people were killed in Mumbai on Tuesday when a wall collapsed as the heaviest monsoon rains in a decade brought chaos to India`s financial capital and surrounding areas.

Scores more were injured when the structure came down around 2am (2030 GMT Monday) in a slum, said Tanaji Kamble, a disaster management spokesman for Mumbai`s local authority.

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 more than 100 flights were either cancelled or diverted from Mumbai airport.

The airport`s main runway was shut after a SpiceJet plane carrying 167 passengers and crew overshot it shortly before midnight Monday.

`Currently secondary runway is in use, our team is trying their best to bring the main runway back in operation and this may take up to 48 hours,` the airport tweeted.

According to Skymet Weather, a private weathertracking agency, large swathes of Mumbai received around 350 millimetres (13 inches) of rain overnight into Tuesday morning, the most in a decade.

The deluge left low-lying areas submerged.

`Everything around us is flooded. It`s scary and the problem persists every year despite government promises,` Vishal Agawane, a 32-year-old resident of the Dharavi slum, told AFP.

Around 1,000 people living close to the city`s Mithi river were evacuated to higher ground as it threatened to burst its banks, said Kamble, the disaster management spokesman.

Train services on Mumbai`s colonial-era rail network, a lifeline for the city`s population, were disrupted due to waterlogged tracks, while motorists were seen pushing cars through flooded streets.

Rescuers were sifting through the debris of the wall that collapsed in a slum area in Mumbai`s north, in the hope of finding more survivors trapped under rubble.

The dead included a 10-year-old girl, who was trapped alive under the debris for hours before rescuers pulled out her body in a 12-hour-long unsuccessful operation.

A local rescue volunteer earlier in the day told the NDTV channel that they heard the girl crying in pain and begging for water.

Building collapses are common during the monsoon, when dilapidated structures buckle under the weight of continuous rain.

Three people, including a toddler, were also killed on Tuesday in Thane district, which borders Mumbai, when a wall collapsed at a school.

Two waiters were electrocuted after rainwater gushed into a restaurant and came in contact with a live wire in Thane. Another person was critically injured.-AFP