The reason for the fire was not known immediately, police said, adding, three fire fighting units and 10 ambulances were pressed into service.
The fire was noticed in one of the manufacturing wings of the factory and it soon spread to other areas. The noise triggered panic among people in the surrounding area and waves of the blast were felt even two km away from the site, forcing officials to stop traffic on Athur road, police said.
As the area was receiving heavy rains, rescue operations could not be taken up in full swing, though the fire had been almost contained, police said.
The licenced unit was working for more than 25 years, police said.