Eight others were reported to have been injured in the four-storeyed building collapse in the city's Dongri area.
The incident occurred at 11 am on Tandel Street in Dongri area, initially killing two persons and trapping over 40 people under its debris.
Following the deadly collapse, Maharashtra Chief Minister Devendra Fadnavis had ordered an investigation into the incident.
Three teams of the National Disaster Response Force (NDRF) are engaged in rescue operations.
Brihanmumbai Municipal Corporation (BMC) Commissioner Praveen Pardeshi visited the spot and took stock of the rescue operations.
Prime Minister Narendra Modi shared his condolences with the families of the deceased.
''Collapse of a building in Mumbai’s Dongri is anguishing. My condolences to the families of those who lost their lives. I hope the injured recover soon. Maharashtra Government, NDRF and local authorities are working on rescue operations & assisting those in need,'' PM Modi said.
(With inputs from agencies)
Eight others were reported to have been injured in the four-storeyed building collapse in the city's Dongri area