Two women and a man were killed when a firecracker factory in the Mohanpur-Sonaria area of South 24-Parganas’ Nodakhali caught fire on Wednesday morning.
The fire at the factory near Budge Budge reportedly followed an explosion at the unit.
Police said the blast took place around 7.30am when workers were stacking packs of crackers in a storage room.
Eyewitnesses said they heard a “huge explosion”, followed by “rushing” balls of fire engulfing a section of the factory.
“A Budge Budge fire tender reached the spot not long after the breakout,” said an official.
Some who were trapped were rescued by the fire brigade.
The deceased were Ashim Mondal, Atithi Haldar and Kakali Midye, all residents of Mohanpur, the police said.
“An investigation is on but no conclusive cause has been ascertained yet, ” said an official on Wednesday afternoon.