An explosion took place in the factory after lightning struck the building and the structure collapsed last evening, Assistant Superintendent of Police Amit Verma said.
Three women working in the factory - 65-year-old Ramjano 40-year-old Farzana and 45-year-old Jamshidi - were killed in the explosion.
Four passers-by were also injured and rushed to hospital.
Verma said the cracker factory was being run unauthorisedly
According to police, over 50 unauthorised cracker factories are operating in the area.
Taking serious note of the incident, District Magistrate Shashi Bhushan Kumar has directed sub divisional magistrates to file a report about unauthorised cracker factories operating in the area.