Investigating officer R.K. Dhamne of Poinad police station said the explosion followed by a fire took place at the Kranti Fireworks Ltd. factory around 3.30 p.m.
"Four labourers died in the blaze and later two more bodies were found," he said.
Due to the impact of the explosion - the cause of which was not immediately clear - some nearby dwellings in Bhaimala village sustained damage.
Seven fire tenders from Alibaug and neighbouring area rushed to battle the blaze which was brought under control later in the evening.
The injured were admitted to hospitals in Raigad, while six who sustained serious burns have been shifted to Sir J.J. Hospital in Mumbai.
Bhaimala is around 10 km from the picturesque beach resort of Alibaug, around 110 km south of Mumbai in Raigad coastal district.