Italian firefighters and Carabinieri police said that the 71-year-old wife of the owner of the family-run factory in the Sicilian town of Barcellona Pozzo di Gotto was among the victims. The owner's son was hospitalized in serious condition.
Police say workers at the depot may have accidentally set off the explosion with welding equipment on Wednesday afternoon.
Safety at fireworks depots has been long debated in Italy, where the production of fireworks is often a family-run business.
Consumers association Codacons says 68 people have been killed in explosions at fireworks firms since 2000.
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