The 35-year-old three-storey 'Shakuntala' building, situated at Bazarpeth in Mumbra area of Thane district, collapsed after midnight when the residents were fast asleep, police said.
Children, including a two-month-old girl, were among those killed in the mishap.
Police rushed to the site at around 2.30 AM and launched relief and rescue operations on a massive scale even as more people were feared trapped in the debris of the building.
Thane District Collector P Velrasu, Police Commissioner K P Raghuvanshi and acting Municipal Commissioner Shaymsunder Patil have gone to the spot while a fire brigade team has also been deployed for assistance.
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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.