Chief Minister Mamata Banerjee ordering a CID investigation into the incident.
"Twelve charred bodies have been recovered from the blast spot, while four injured have been admitted to hospital," IGP (Western Range) S N Gupta told PTI.
The house owner Ranjan Maiti has been arrested, he added.
Police said the factory was illegal and the blast took place shortly before 10 PM last night and the raging fire has been put out.
All the victims were employees of the factory who were brought from Murshidabad district, police said.
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To a question if the incident was like the Burdwan blast that took place in October last year and claimed the lives of two suspected Jamaat-ul Maujahideen Bangladesh terrorists, Gupta replied in the negative. "It is (Pingla blast) an accident in a cracker factory."
Asked if any central probe team, specially the NIA, had visited the spot or contacted him, Gupta said, "The question does not arise since it is a case of accident in a cracker factory."
The Chief minister, who ordered a CID probe into the explosion, wondered, "How could so many firecrackers be prepared at one place and how so many explosive substances were accumulated in one place ?"
"I ask all Green police (civic police) personnel in all villages to keep a watch on such activities and to inform the local police station if they find explosive substances being accumulated at any place," she said at a programme at Namkhana in South 24 Paraganas district.