Six women were killed and 20 others injured after a four-storeyed building collapsed at Bhiwandi town in Thane on Tuesday night, police said.
Many others are feared trapped in the debris, they said adding that rescue operations continued late into the night.
The building, which stood at the Gautam Compound Navi Basti, reportedly housed nearly a hundred families. It was originally a two storey building and two floors, possibly illegally, were added on to it later, police said.
Over a dozen fire engines have been pressed into service.
The rescue operation is being supervised by district collector A L Jarhad, officials said.
The deceased have been identified as Mashid Hakim Shaikh (23), Sahana Jaffar Shaikh (18), Mehbooba Shaikh (45), Sufali Shaikh (80), Safia Illias Shaikh (30) and Kalina Shaikh (22).