A fire broke out following the explosion at around 2 AM in the single-storey aluminium moulding facility at Sakinana in suburban Andheri. The unit was reportedly operating without necessary permission.
Due to the blast, the single-storey structure fell on a wall of the house where six members of the family were sleeping, trapping them under debris, they said.
The deceased were identified as Sukha Patel (60), his son Ganesh, daughter Bharti Rathod and her two children Manisha and Neha. Another family member, Mangesh Patel, was injured, they said.
Teams of Maharashtra ATS and Mumbai Police also visited the spot to ascertain if the incident was due to the handiwork of terror elements. They later ruled out terror angle.
"The explosion may have occurred due to aluminium casting pressure, though the exact cause is not yet clear," a Fire Brigade official said.