The operation was uncovered after a routine traffic stop resulted in the seizure of over 168 kilograms of drugs brought into Arizona from Mexico through the narrow tunnel.

The drugs included 118 kilograms of methamphetamine, six grams of cocaine, three kilograms of fentanyl, 13 kilograms of white heroin, and six kilograms of brown heroin.

A search then revealed the tunnel - 8 inches in diameter, 22 feet deep, and nearly 600 feet long - which started in the former KFC restaurant’s kitchen.

Police are unsure how long the tunnel has been in use, KYMA News reports.