The tunnel lies on the eastern side of the road between Calcutta University ground and BNR Sports Club in the heart of the city.
One of Kolkata's biggest and busiest streets, Red Road, has been keeping a secret.
A six feet-long and three feet-wide wide tunnel has been discovered, the work, according to the local police, of drug addicts.
A senior Kolkata Police officer said the offenders were trying to steal copper wires and steel plates laid underground for electric connections. The material would fetch a lot of money on the black market.
A senior Kolkata Police officer said the tunnel was a handiwork of drug addicts.
No one has been arrested so far.
Senior officers of the force rushed to inspect the tunnel off the road, which is in a high security zone as it passes through Fort William, the headquarters of the Army's eastern command.
Rajeev Mishra, joint commissioner (HQ), Kolkata Police, said, "Though some investigations are on, no terror angle has been found. We are checking antecedents of the five people arrested in 2013 for digging a similar tunnel. As of now, it seems to be an attempt by drug addicts to steal underground wires and sell them to make some money."
In December 2013, another tunnel dug illegally in the area was found and five persons were arrested in this connection.