Mumbai, India's Maximum City, is being pounded by record rain. The heaviest rain in the city in 24 hours in almost 15 years has caused more than 27 deaths.

At least 21 people were killed and over 60 others injured when a 10-meter (35-foot) wall demarcating an urban forest collapsed during the night in Mumbai, police officer Ravinder Howle said.

Nine deaths were caused by two wall collapses elsewhere in Maharashtra state.

Six migrant construction workers were killed and five injured when a wall collapsed on their tin-roofed huts in Pune early on Tuesday, an officer in the city's Police Control Room said.

In Thane district, a school wall collapsed and fell onto huts, killing three people and injuring one, said Lakshman Pawar, a local civic official.

Howle said two men died after they got trapped in a submerged car, raising the overall death toll in Maharashtra to 32.

Rescue teams with sniffer dogs were searching the area afterward, and rescuers from the Indian navy also fanned out to help and rescue residents of the waterlogged city.

Monday's rains also flooded roads in Mumbai and covered train tracks.

According to reports, Mumbai received around 375 millimetres (13 inches) of rain on Monday, making it the maximum July downpour that the city has seen over a 24-hour period, breaking the record of 1974. It was the second-highest rainfall in a 24-hour period in 44 years, according to weather-tracking agency Skymet.

Rains subsided by midday Tuesday but weather officials predicted more heavy rain in the next three days.

Central Railway in a tweet said that "nature's fury" made operating trains a "safety hazard" in some areas. Train services were running only partially on Tuesday after thousands of passengers were stranded overnight. Millions of passengers commute daily on a network of famed railways in Mumbai.

Long-distance trains from different parts of India, expected to reach Mumbai, have also been stranded at various locations en route, details of which were awaited.

The city has witnessed incessant rainfall over the past few days and floodwaters have entered homes. A public holiday was declared for Tuesday and the Maharashtra government said only emergency services would be functional.

Maharashtra chief minister Devendra Fadnavis tweeted: "People are advised to stay indoors unless there is any emergency."

TV channels showed videos of submerged cars and water flowing through ground floors of some residential buildings.

A SpiceJet flight -  SG6237 - skidded off the main runway at the Mumbai airport and blocked it after overshooting late Monday night, and flight operations were partially restored on Tuesday. At least 50 domestic and international flights were diverted and 50 other flights were cancelled.

Till Tuesday noon, at least 55 incoming flights were diverted, including 26 international. There were 13 go-arounds, and cancellations of 18 incoming flights including four international and 24 departures including four international, said a spokesperson for Mumbai International Airport Ltd (MIAL).

Road traffic also continued to be sluggish for the second consecutive day in the city and the suburbs as many areas were waterlogged and the subways in Andheri, Jogeshwari, Vile Parle and Dahisar flooded.

A road caved in near a construction site in Chandivali and locals claimed that some people may have been washed away in the incident. A few vehicles and autorickshaws were stuck in the cave-in, which was at least 10 feet deep, said a local resident Pradeep Menon.

"In the past 12 hours, the city has received an unprecedented 300 to 400 mm rain, the highest in the past decade. The existing drainage systems are unable to cope with such a heavy downpour, coupled with a high tide this afternoon," Fadnavis told mediapersons.

The Indian Navy deployed rubber boats and a team of naval divers from INS Tanaji, armed with lifebouys, life-jackets and food packets, rescued around 1,000 people stranded in Kranti Nagar slums of Kurla.

Fadnavis visited the BMC Disaster Cell and those injured in the Malad wall crash tragedy in hospitals.

Since dawn, heavy rain continued to lash the city, Thane, Raigad and Palghar districts with the IMD forecasting more rains till Friday, besides continuing downpour in Nashik and parts of Western Maharashtra, Ratnagiri and Sindhudurg.