India building collapse near Mumbai kills 29
Many others are feared trapped beneath the seven-storey building in Thane, Indian media report, quoting officials.
Police said the building was being constructed illegally and four floors were already occupied.
Building collapses are common in India. Poor construction material and practices are often blamed.
A section of the building collapsed on Thursday evening bringing the entire structure down, a police official in Thane, Maharashtra state, told AFP.
He said nine children were among the dead.
Rescue efforts continued through the night.
Police Inspector Digamber Jangale said at least 54 people had been injured.
Most of the victims were construction workers who were staying in the building, he added.
One witness, named only as Ramlal, said the building appeared to tilt before quickly collapsing.
"The building collapsed like a pack of cards within three to four seconds," he said
In December at least 13 people died when part of a half-constructed building collapsed in the Wagholi area of Maharashtra, according to BBC.
Last September at least six people were killed when a building collapsed in Pune city in Maharashtra.