Fire brigade sources said 20 fire-tenders were engaged in fighting the blaze, which is still raging in the factory site situated in Cossipore police station area.
The police said the area had been cordoned off and traffic diverted to facilitate fire-fighting, which led to a huge traffic snarl in the surrounding areas.
An adjacent godown to store paint produced in the factory also caught fire.
There was no report of any casualty or persons being trapped inside the factory, the police said.