The underground passage was uncovered on Thursday, about 650 feet south of a sophisticated drug tunnel the length of six football fields that was found on Nov 2.
US border agents said on Friday they had found a half-mile-long tunnel under the US-Mexico border and seized a significant amount of marijuana at the San Diego area warehouse where it ends.
The underground passage was uncovered on Thursday, about 650 feet south of a sophisticated drug tunnel the length of six football fields that was found on Nov 2.
That tunnel, which measured 1,800 feet and was equipped with a rail system, lighting and ventilation, yielded some 30 tons of marijuana, one of the largest such seizures on the border in recent years.
The new shaft links a private home in eastern Tijuana, Mexico with a warehouse in Otay Mesa, a largely industrial district of San Diego.
Investigators with the San Diego Tunnel Task Force say they found bales of marijuana in a trailer truck and believe there is more in the passage. They were expected to release more details at an afternoon press conference.
US Border Patrol spokesman Michael Jimenez said the tunnels are generally dug by hand, a long process because the clay soil has to be removed without drawing attention.
Mexico is in the grip of a raging drug war that has killed more than 30,000 people south of the border since December 2006, when President Felipe Calderon launched a crackdown on powerful drug gangs.
Mexican cartels have bored scores of tunnels under the US-Mexico border in recent years to beat ramped-up security at ports of entry and the rugged spaces in between. Nearly all of them linked cities on either side of Mexico's border with California and Arizona.
Tijuana is the principal gateway for drugs entering California from Mexico. Last month, authorities there seized more than 100 tonnes of marijuana valued at more than $340 million in Mexico's biggest pot haul to date.
Several federal and local police agencies are part of a special task force to search for tunnels running under the border in the San Diego area, which has soft, loamy soil that lends itself to tunneling.
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