Officials said 22 men, eight women and three children died when the residential building gave way on Thursday morning in the densely populated area of Bhendi Bazaar following heavy rains.
The 117-year-old building had been declared unsafe and was due to be demolished as part of a redevelopment project that is transforming Bhendi Bazaar, a scruffy colonial-era market.
"Overnight we pulled out 15 bodies, taking the total death count to 33," Tanaji Kamble, a disaster management spokesman for Mumbai's civic authority, told AFP.
The dead included a 12-year-old boy and two girls aged 11 and 14, he added.
Twelve other people were being treated for injuries at a local hospital, Kamble said.
Rescuers were still picking through the debris on Friday morning in the hope of finding more survivors, 24 hours after the dilapidated building collapsed in one of Mumbai's most historic districts.
Rescue workers and residents look for survivors at the site of a building collapse in Mumbai, after days of heavy rain swamped the city (Getty Images) Source: Getty Images
It was the latest deadly housing collapse to strike the city, highlighting poor construction standards in India, and came following severe rains that have wreaked havoc in many parts of South Asia.
Building collapses are common in Mumbai, especially during the monsoon season from late June to September, when heavy rains lash the western Indian city, weakening poorly built structures.
Millions are forced to live in cramped, ramshackle properties because of spiralling real estate prices and a lack of housing for the poor.
In 2013, 60 people were killed when a residential block came crashing down in one of Mumbai's worst housing disasters.
Thursday's collapse came after flooding in the city killed 10 people.
