The 35-year-old Shakuntala building, situated at Bazarpeth in Mumbra area of Thane district, collapsed after midnight when the residents were fast asleep, police said.
The building constructed in the 1980s was owned by Balaram Mhatre and had nine families staying in it.
Police rushed to the site at around 2.30 am and have launched relief and rescue operations.
Many are still feared trapped in the debris of the building, police said.
“We got a call from Mumbra around 2.30 am and four fire engines were rushed to the spot. The rescue work is on,” said a fire officer from Wagle estate fire brigade station.
"Though the building was declared dangerous by the Thane municipal corporation (TMC), it had nine families staying in it. The ground floor had shops while the second floor was empty. The families stayed on the first and third floor,” he added.
“The injured have been shifted to Kalsekar Hospital and Chhatrapati Shivaji Hospital in Kalwa,” said an official from TMC’s disaster management cell.
Thane District Collector P Velrasu, Police Commissioner K P Raghuvanshi and acting Municipal Commissioner Shaymsunder Patil rushed to the scene while a fire brigade team has also gone there for assistance.
Six of the deceased have been identified as -- Mahek Muddasar Punjabi (2 months), Mohamad Rehan Jilani Faruki (25), Usna (4), Abdul Karim Shaikh (30), Tasmiya Makdum Shaikh (3) and Shakir Abdul Karim Shaikh (6).
On June 10, a four-storey building collapsed at Mahim in Central Mumbai in which 10 people were killed and six injured.
Prior to this, a building crashed on April 4 at Shil-Phata near Mumbra in Thane district which claimed as many as 74 lives and left over 60 injured.
With Agency inputs