AFP reports citing police.
A section of the seven-storey building collapsed on Thursday evening before the entire structure came down, a senior officer in the police control room of Thane district told AFP.
"Twenty-seven people have died so far, of which seven are women and nine children," said the officer who did not want to be named.
Teams from the National Disaster Response Force and other rescue workers were trying to clear the debris from the site amid fears there may be more people trapped in the twisted pile of of concrete and steel.
The victims were workers and members of their families who were living in some of the still-unfinished areas of the building.
The Hindustan Times daily said the builders may have flouted norms.
"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.