This is the fourth tragedy since April this year.
The building -- 'Piyush' -- collapsed at around 6.30 am, civic authorities said, adding that most of those trapped in the rubbles were local vegetable vendors.
The civic authorities had vacated the building two years back as it was in a dilapidated condition.
Shiv Sena MLA from Dahisar Vinod Ghosalkar and local Congress MP Sanjay Nirupam visited the crash site.
Ghosalkar said the building was vacated two years ago after it was declared 'dilapidated' by the civic authorities.
"It was to be redeveloped, but was stuck in litigation due to a dispute between the builder and the flat owners. As the redevelopment was stuck, local workers and vendors had taken shelter in the building," he said.
Nirupam said the building was nearly 30-years-old and could not be redeveloped as the builder had not issued conveyance deed to residents.
Earlier on April 4, an unauthorised building had collapsed at Shil-Phata near Mumbra in Thane district, claiming as many as 74 lives and leaving over 60 injured.
On June 10, a portion of a four-storey building collapsed in Mahim, killing 10 and injuring six. On Friday, a 30-year-old building collapsed in Mumbra in neighbouring Thane district, killing 10 and injuring eight.