The seven-storey illegal structure collapsed on Thursday evening, creating a mangled heap of steel and concrete of about eight metres (26 feet) high that rescuers and local residents struggled to cut through, officials said.
Rescue efforts continued through the night, with diggers and steel cutters employed to reach victims who were carried away on makeshift stretchers. Limbs protruding from the wreckage were a grisly sight in some areas.
As emergency workers combed the rubble for survivors in front of a huge crowd of onlookers, two toddlers were pulled out alive to cries of "God is great" and cheers and clapping, an AFP photographer at the scene said.
"Thirty have died and at least 55 others are injured," said Sandeep Malvi, a spokesman for the local municipal administration in Thane, where the building collapsed about 35 kilometres (20 miles) from the centre of Mumbai.
Among the dead were at least seven women and nine children, police said.
Local police commissioner KP Raghuvanshi said his force had registered a case of causing death by negligence against the builders. "There are two builders and we are looking for them," he told reporters at the scene.
Many of the victims were migrant labourers who had come to Mumbai to find work on building sites, typically earning as little as two-four dollars a day. They often bring their wives and children, who live on-site.
Others had already moved into homes in the block, including schoolgirl Hasina Shaikh and her family, who were living on the fifth floor.
"I had just returned from school and was changing my clothes when the building started shaking and came down on us. When I regained consciousness later, I was in the hospital," she told the DNA newspaper.
Shaikh said she did not know the whereabouts of her relatives.
Mohammed Anwar, 36, witnessed the accident while his father-in-law, a carpenter, was inside it working. "I saw the building collapse like a pack of cards," Anwar told the Mumbai-based paper.
The local civic administration said it was probing the incident and would check other new structures built recently in the vicinity, a middle-class commuter area with modern-style residential blocks.
"The building (that has collapsed) was an unauthorised construction. We are going to investigate thoroughly into this and prepare a report," Malvi from the Thane municipal corporation told AFP.
The Hindustan Times daily said builders may have ignored construction regulations.
"Seven floors were built in merely three to four months. It was bound to collapse due to the inferior construction material used by the builders," the paper quoted the local head of the disaster management cell as saying.
Building collapses are a common occurrence in India, where a booming economy has led to a mushrooming of multi-storey structures which are often unauthorised and flout safety laws.
In February, the collapse of a flyover bridge being built at Mumbai's main airport killed three people and injured another seven.
In one of the worst such accidents of recent years, 69 people died and more than 80 were injured in November 2010 in New Delhi where a residential building under construction collapsed, trapping families in the lower floors.
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@JS if something gets mention in the pakistani newspaper, could have pakistani connection. any way, the builders were indian muslims. do you want to see any connection with it.
http://timesofindia.indiatimes.com/city/thane/28-killed-as-illegal-tower-crashes-in-Mumbra/articleshow/19393443.cms
@I am a Khan: "Will the illegal builders be arrested for this tragic loss of life? I doubt it…" Don't! They will not only be arrested but surely serve time. It may take a little long but they can never escape!
Have the indians not issued a press release as yet, that the architects had connections in Pakistan!
Sad. May Allah grant the affected families the fortitude to bear the loss. Will the illegal builders be arrested for this tragic loss of life? I doubt it...