US authorities discover drug smugglers' Mexico-US border tunnel

The tunnel lies 35 feet under ground and runs the length of nearly six football pitches

Mexican soldiers guard the warehouse where the tunnel begins (AP)

US authorities have discovered one of the most sophisticated tunnels ever designed to smuggle drugs across the Mexico-US border.

The passage that runs between Tijuana, Mexico, and San Deigo in the US is equipped with an electrical rail system, lighting and ventilation.

Seizures by the police linked to the tunnel include over 8 tonnes of marijuana and 327 lbs of cocaine, according to court records.

Police say three men who worked as drivers were charged with possession of the illicit drugs with intent to distribute. US lawyer Laura Duffy says it is likely the men will face between 10 years and life imprisonment if they are found guilty.

The four foot high tunnel lies 35 feet under ground and runs the length of nearly six football pitches. Its zigzagging shape suggests the excavators veered off course a number of times.

The passageway links warehouses in Tijuana and San Deigo’s Otay Mesa industrial area where a large number of the large stores stand, making it easy to conceal trucks filled with drugs.

The San Diego warehouse was placed under surveillance by US federal agents after they were tipped off by an informant who told them about the sale of drills and other construction equipment in August and September.

The drugs were seized before they could be sold.

Mexican drug cartels have had to use ultra-light aircraft, small fishing boats and tunnels in response to heightened US border security on land. Over 75 underground passageways, mostly designed to smuggle marijuana, have been found dotted across the border since 2008.

The tunnel is the eighth major passage discovered in San Diego since 2006, but the first in the area that has been used for cocaine. The clay-like soil in San Diego makes it easy to dig tunnels into the ground.