US officials have discovered an underground tunnel about the length of five football fields used to smuggle drugs from Mexico to a warehouse in California.
It is not known how long the secret passage, which has a railway line, ventilation systems, electricity and reinforced walls, has been operating.
Investigators found the tunnel after staking out a house used to stash drugs in the Mexican border town of Tijuana and stopping vehicles near the warehouse in Otay Mesa, south of San Diego.
They found boxes full of cocaine, according to a federal criminal complaint filed in San Diego.
The warehouse was on a busy street by day but quiet by night, with armed guards guarding a small shaft with a ladder leading down into the tunnel.
Officers raided the warehouse and found no drugs, only a tunnel opening dug into the cement floor.
The passage, discovered last week, traveled a third of a mile (532 m) to Tijuana and was 4 feet (1.2 m) wide.
Six Southern California people, ages 31 to 55, have been charged with conspiracy to distribute cocaine.
Authorities seized 799 kg of cocaine, 75 kg of methamphetamine and 1.6 kg of heroin as part of the investigation.
“There is no more light at the end of this narco-tunnel,” said Randy Grossman, attorney for the Southern District of California.
“We will remove any underground smuggling routes we find to prevent illegal drugs from reaching our streets and destroying our families and communities.”
The passage was discovered in an area where more than a dozen other sophisticated tunnels have been discovered over the past two decades.
Authorities have not linked the latest tunnel to any specific cartel.