Six people have been arrested on drug charges after US and Mexico authorities discovered a drug smuggling tunnel running between the two countries.

       US authorities on Monday announced that a drug smuggling tunnel — running about 1,744ft in length and 61ft deep — had been found on Friday.

       A haul of drugs containing 1,762lbs of cocaine, 165lbs of meth and 3.5plbs of heroin were seized in connection with the investigation, worth about $25m on the street.

       It was not clear how long the tunnel connecting the Mexican border city of Tijuana and San Diego, California, had been used by drug smugglers.

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       Reports said the tunnel was found by investigators who conducted traffic stops on vehicles travelling through San Diego, which connected them to a warehouse with the tunnel.

       Authorities said rail and ventilation systems, as well as electricity and reinforced walls were installed at the tunnel. Nor was it far from other similar tunnels found in the past 20 years.

       Many of the tunnels have made border walls redundant when attempting to limit cross-border drug smuggling.

       The entrance to the tunnel has been guarded since Friday

       (AP)

       “There is no more light at the end of this narco-tunnel,” said Randy Grossman, US attorney for the Southern District of California, in a court filing.

       “We will take down every subterranean smuggling route we find to keep illicit drugs from reaching our streets and destroying our families and communities.”

       The six people arrested ranged in aged between 31 and 55, all of whom were charged with conspiring to distribute cocaine. All are Southern California residents.

       Additional reporting by The Associated Press.