At least 30 people died in three Mumbai suburbs after several houses collapsed when heavy rain triggered landslides, officials said on Sunday.
Rescuers used their hands to dig up the ground in an attempt to find survivors, local television showed, as authorities said more people could be trapped inside the debris.
Emergency workers carried the injured through narrow lanes on makeshift stretchers.
Several areas of Mumbai have been hit by floods because of heavy rain over the past 24 hours, crippling India's financial capital.
The mega-city and the coast of India's industrial Maharashtra state are expected to receive heavy-to-very-heavy rainfall in the next four days, the weather department said in a statement carried by Reuters.
"We'll take the decision to shift the people who are living in a dangerous situation to permanent settlements immediately," said Nawab Malik, a state cabinet minister, according to a tweet by news agency ANI.
Trapped under the rubble
Within the past 24 hours, authorities have reported 11 incidents of houses or walls collapsing in the Mumbai area, officials said.
In one neighbourhood, about half a dozen shacks located at the base of a hill collapsed on top of each other, they said.
In another incident, a falling tree demolished a wall in the eastern suburb of Chembur during Sunday's early hours, burying nearby residents, the National Disaster Response Force said.
Seventeen bodies have been recovered from the rubble, it said, amid continued efforts to rescue survivors.
"In the adjacent house, I saw a small girl who was trapped in the debris. She was shouting 'save me, save me'," Firoz Khan, who was caught up in the downpour in Chembur, told AFP.
"Her body was trapped in the mud. Somehow, I managed to pull her out. She had injuries in her legs. I narrowly survived this collapse."
Another resident, Manda Gautam Pradhan, said she had seen "rocks and mud... gushing down the hill along with the rainwater".
Torrential rain, especially during India's July-September monsoon, often triggers the collapse of buildings, especially older or illegally built structures.