Police said they suspect that a crude bomb was hidden there which went off when they struck it with a spade.
One person was killed and two others injured after an explosion outside a factory in North Kolkata's Kashipur.
The blast took place around 3 pm when some workers were cleaning the compound, police said.
Police said they suspect crude bombs were hidden in the undergrowth in the factory compound by local criminals.
Those cleaning the area may have hit them accidentally with a spade and triggered the blast, they said.
Police are on the spot with sniffer dogs to check if there are any more bombs in the area.
The factory reportedly makes parts for ships.