Five others were injured in Monday evening's blast at the Eagle Fireworks factory in Sangli district.
It was not immediately clear how the fire started.
Accidental explosions are common at Indian fireworks factories, which provide fireworks for weddings, festivals and other ceremonies.
In 2012, 34 people were killed and 30 others injured in a massive blaze at a fireworks factory in the southern Tamil Nadu state.
The BBC Hindi's Devidas Deshpande in Pune says that the latest explosion in Kavathe Ekand village was so powerful that it was heard at least five kilometres away, and the debris of the factory was scattered far and wide.
The mother and the son of the factory owner were among the dead, while his brother and three workers were seriously injured.
The village has many households making firecrackers for local religious festivals and such incidents have been reported before.
Some 25 people have been killed in at least six such incidents in the village in the past few years, our correspondent says.
At least nine people have been killed in an explosion at a fireworks factory in the western Indian state of Maharashtra, police say.