The find, by Mexican officials searching for the killers of a Catholic cardinal shot dead at Guadalajara airport, shocked authorities on both sides of the border engaged in a war against drug traffickers.
Police said that the quarter- mile tunnel runs from a site close to Tijuana airport in Mexico to an industrial zone in southern San Diego, California, and was about 50ft from completion. It was found beneath a warehouse, and appeared destined for a second warehouse being built on the other side.
The Mexican authorities believe that it was the work of a cartel headed by Joaquin 'El Chapo' Guzman, one of the country's most powerful mafia godfathers whom they claim was the intended target of last month's shoot-out in Guadalajara. Prosecutors maintain that assassins from a rival gang shot the cardinal, Juan Jesus Posadas Ocampo, after mistaking him for the drugs baron.
The drugs traffickers appear to have planned to smuggle their wares to the US via the tunnel, then distribute them by lorry from the San Diego industrial zone - an area crowded with warehouses where heavy vehicles come and go around the clock. One US official said it was mind-boggling: 'They could have smuggled multi-ton quantities of cocaine . . . and it would have gone undetected.'
The discovery comes as the US authorities agonise over the likelihood that the proposed North American Free Trade Agreement will make it more difficult to control drug running. The Mexican cartels are believed responsible for smuggling 70 per cent of the cocaine that enters the US each year.
The 'drug-tunnel', which cost an estimated dollars 1.5m ( pounds 970,000) to dig, is about 5ft high and 4ft wide. It was discovered after Mexican agents found documents in one of 15 traffickers' 'safe-houses' unearthed in Tijuana since the search for the cardinal's killers began. They have also recovered weapons, including grenade launchers. This is the second cross-border tunnel to be discovered - a smaller one was found in 1990 running into Arizona.Reuse content