A road caves in following heavy monsoon rains, at Sangharsh Nagar in Mumbai

In just 24 hours, Mumbai has witnessed the highest rainfall - over 370 mm - and the worst in July since the deluge of 2005. Overnight, a wall collapsed in suburban Malad, killing 21; heavy rain flooded the airport and paralysed local train, the lifeline of India's commercial capital.

With excessive rain battering the city, Navy teams were out before the crack of dawn and the rescue operations begun. Around 1,000 people living close to Mithi river were also evacuated to higher ground as it threatened to burst its banks.

Chief Minister Devendra Fadnavis asked people to stay at home today except for emergencies in and around Mumbai. A public holiday was declared in the city as well.

Through the day, over hundred flights have been delayed or cancelled after a SpiceJet flight skid off the main runway last night, forcing it to shut down.

In low-lying areas, especially Sion, Kurla and Vikhroli, water covered the rail tracks, disrupting the city's lifeline. But by late morning, Western Railway trains running between Churchgate and Virar stations resumed with 20-25 minute delays. However, Central Railway trains running between Thane and Mumbai CST resumed late in the evening by 5.

Mumbai's civic body, the Brihanmumbai Mumbai Corporation has been trying to get the excess water removed from the streets. 1,400 pumps operated for much of the day at 53 flooded spots.

The weather department expects the rainfall to slow down, although the forecast is still of heavy rainfall for another 24 hours.

"Forecast for today is that the warning has come down from Level 3 and we are expecting intermittent showers today and tomorrow but warning is only for today," KS Hosalikar, Deputy General, Met Department, Western Region, told NDTV.