MEXICAN officials have discovered the deepest tunnel ever gouged under the US border, equipped with electricity and ventilation and concealing two tonnes of cannabis.

The scale of the tunnel — the 21st discovered in more than four years — stunned authorities, who said that the passageway revealed the lengths to which smugglers would go to evade detection.

The underground smuggling route began near the airport in Tijuana, Mexico, and ended 2,400ft (720m) away in a warehouse in San Diego in the US, Michael Unzueta, special agent in charge of US Immigration and Customs Enforcement in San Diego, said. It was unclear how long the tunnel had been in operation, he added.

The 60ft-deep (18m) tunnel had a concrete floor, electric lights that ran down one of the hard soil walls and air piped from the surface. An adult could nearly stand in the 5ft-high (1.5m) shaft. “It was like being in a cavern or a cave,” Mr Unzueta said. “It’s just huge, absolutely incredible.”

John Fernandes, the special agent in charge of the San Diego office of the Drug Enforcement Agency, said that he suspected that the tunnel was the work of the Arellano-Felix drug-smuggling syndicate in Tijuana, or another drug cartel. He said that tougher enforcement above ground had forced smugglers to dig below.

Mexican investigators found the tunnel entrance on Tuesday inside a warehouse about 150 yards (136.5m) south of the border. A 6 by 10ft shaft equipped with a pulley dropped about 75ft to the entrance. The next day US authorities located the exit on the American side within a warehouse.

Mexican authorities allowed reporters and photographers inside the tunnel on Wednesday. Near the entrance, authorities were seen weighing bales of what appeared to be marijuana. Hundreds of packages wrapped with brown packing tape were stacked up to the ceiling. It was unclear whether the tunnel was designed to sneak people or drugs other than marijuana into the US, Mr Unzueta said.

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