The Kesarbai Building in south Mumbai's Dongri area collapsed at around 11.30 a.m.
Three teams of National Disaster Response Force (NDRF) are still engaged in rescue operations as it is feared that some people are still buried under the debris of collapsed building.
The building was located in a narrow lane in a congested area of India's financial and entertainment capital.
"We have moved five of our vehicles to the spot".
"We have been visiting the BMC (Brihanmumbai Municipal Corporation) for funds to fix the buildings".
It did not feature in the MHADA's annual list of risky buildings, which is released before the start of monsoons every year, according to officials.
Tanaji Kamble, disaster management spokesman, also told AFP news agency that 40 others were "under the debris" following the incident on Tuesday in Mumbai's crowded Dongri area.
As the building collapsed it sent shock waves shaking adjacent buildings.
Maharashtra state's top elected official, Devendra Fadanavis, told reporters that 15 families were living there.
Prime Minister Narendra Modi expressed sadness over the collapse of the four-storey building and said that the incident is deeply anguishing. For some like Mohammad Alam, who had rented out a room on the second floor of the collapsed structure, it was a lucky escape.
As a precautionary measure, the police evacuated an adjoining building. She said, "My sister had just shifted to the building around a year ago".
Ambulances could not reach the site and had to be parked around 50 metres away.
Some part of the building was left standing after the collapse. "Rescue operations are ongoing and our main focus is find those trapped", he added. He also said compensation for victims will be announced only after the cause behind the collapse was established.