Indian Broadcasting Network reported officials said Friday the death toll, which included 22 children, was expected to go higher. Another 62 people were injured, the network said.
Municipal Commissioner R.A. Rajeev said the seven-story building was built illegally on forest land.
"We had repeatedly asked the forest department to take action. We had asked MSEB [Maharashtra State Electricity Board] to cut electricity to the building," he said. "We have issued total notices to about 250 illegal buildings in this belt. We try forcible removal. It is not easy."
The building in the suburb of Mumbai, which had people living in it while still under construction, toppled about 6:30 p.m. Thursday, The Times of India reported.
Rescuer Sayed Sadiq said people were living on the first four floors, and construction was under way on the sixth and seventh floors.
Thane legislator Ramesh Patil said the construction of the building was unauthorized and it was unfit for occupation.
Police inspector Digamber Jangale told the BBC the use of substandard building materials was likely the cause of the collapse, and that the eighth floor of the building was under construction when the building gave way.
Daighar village police said they were attempting to locate builders Salil and Khalil Jamadar and intend to charge them with culpable homicide not amounting to murder, the Press Trust of India reported.