Ten fire engines were sent to the spot to assist in the rescue operation. Eight teams were also in the spot to rescue those trapped under the debris.
The BMC (Bombay Municipal Corporation) building was mainly inhabited by its tenants. Civic official said it was old and not well-maintained.
Mumbai and its surroundings have seen a series of building collapses in the recent past, the worst being the Thane tragedy in April in which 74 people, including 18 children, were killed.
In Mumbai, it is the second major collapse after the building collapse in Mahim in June in which ten were killed.