CNN-IBN and other television stations reported that the fire began as people were working at the manufacturing plant in Ujjain in Madhya Pradesh state.
The reports said more than a dozen people had suffered injuries and were in hospital.
CNN-IBN television said that the death toll was expected to rise.
No further details were immediately available.
Many Indian cracker factories are makeshift, sometimes even in people’s homes, and they often employ children.
There are fatal accidents nearly every year as people toil in congested, unsafe conditions.
Factories start producing crackers months before the nation’s biggest Hindu festival, Diwali, or Festival of Lights, when people set off fireworks in celebration.
Diwali falls in either October or November each year, depending on the cycle of the moon.