Police said the members of the gang wore masks and were wielding sickles and knives. They tied up the security personnel and locked them inside a room after snatching away their mobile phones by threatening with weapons.

The ill-fated firm, Hi-Tech Mineral Industries Covai Private Ltd near Omalur, which was into manufacturing alloy from iron ore remains shut over the last seven years after incurring heavy loss. Also, the industry spread over an area of 70 acres is under the possession of the bank over the last three years for defaulting on payment of loan. Due to lack of maintenance, dense shrubs have grown up in the sprawling campus.

Police said the masked gang of around 20 men had arrived in a lorry and tied up the 11 security personnel deployed by a private agency and looted copper plates, transformers, electric items and other valuables worth about Rs 1 crore. Police however, said that they are yet to know the exact value of the stolen goods.

“After preliminary inquiries, we suspect the role of insiders in the daring robbery. They have taken more than five hours to load the valuables on to the lorry,” police said.

The incident came to light early on Monday when people in the neighbourhood suspected something suspicious and informed police. Then, police rescued the locked up security personnel from a room.

Moreover, an unresolved dispute over jurisdiction of the crime spot by the police of Karuppur and Omalur stations led to a joint team from both stations probing the case further.