Several thousands of individuals, social groups, housing societies, Parsi sanatoria, gurudwaras, temples, mosques and dargahs, churches and NGOs entered the fray as the extent of nature's fury became clear.
Appeals started trickling on social media like WhatsApp, Twitter and Facebook. There were also SMSs asking people to move to the nearest place of shelter for a warm cuppa, snacks and even meals and a comfortable nest during the pouring evening on Tuesday.
Thousands trooped down to the main roads, highways and arterial roads inviting or offering people hot beverages and snacks, some giving their mobile phones or chargers to help the stranded to make calls to their anxious relatives.
Many government and private offices grabbed the opportunity to earn the goodwill of their staffers amid dampened spirits.
Even Ola jumped in to help stranded people.
Right from Mantralaya and other offices, the Bombay High Court and other courts, the Indian Navy, private firms, corporates, call centres and BPOs, small offices, factories, workshops and even neighbourhood shops turned into veritable refugee centres for their employees and outsiders slugging it out in neck-deep mucky floodwaters.
Railway terminals and major stations, BEST and State Transport depots and even Chhatrapati Shivaji Maharaj International Airport turned into resting grounds for thousands, scenes reminiscent of the great Mumbai floods of 2005 when the city notched a staggering 900 mm of rainfall on a single day.
Grounded by erratic flight operations, incoming and outgoing passengers armed with luggage slept blissfully on conveyor belts and on the floor at the airport though airport authorities had arranged shuttle buses to Andheri.
In the city and suburbs, several restaurants and eateries, earned praise when managers and waiters stood on the roads distributing water, tea and coffee as well as snacks to the people.
Indian Navy personnel went about in trucks distributing foods packets, volunteers of Leo Clubs, Jain youth groups, Samast Mahajan and Dawoodi Bohra Jamaats were active all over the city helping people, said social worker Anil Galgali.
Bollywood actor Boman Irani sent out of a series of messages indicating shelters in Dadar Parsi Colony, Dadar Gurudwara, sanatoria, halls and other locations with full details to help the stranded.
Scores of Ganeshotsav associations (Mandals) similarly chipped in to shelter and feed those in need in their sprawling marquees.
Mumbai Police displayed a humane face in different parts of the city with its personnel distributing food packets, helping people to safety from flooded localities and engaging in general bonhomie with the public.
Thousands of individuals flooded social media with WhatsApp invitations asking people to take food and rest. Many warmly welcomed absolute strangers into their homes in flats, chawls and high-rise apartments.
The popular menus at most places were tea-coffee-soups, bread-butter-jam, piping hot noodles, vegetable sandwiches, vada-paav, upma, sheera, poha and biscuits. Some places served dal with rice or chapatis or readily available canned foods.
It was only much later that Shiv Sena's Aditya Thackeray and Bharatiya Janata Party's Raj Purohit and other parties besides individual politicians initiated relief efforts.
On Wednesday, Shiv Sena President Uddhav Thackeray, whose party runs the BrihanMumbai Municipal Corporation, will take stock of the alleged failures of the civic body to anticipate and handle the crises effectively for a second time in 12 years.
There was widespread criticism of the ruling party in the civic body and corporators for their failure to mitigate the woes of millions of Mumbaikars, barely six months after the Shiv Sena was voted to power.