Authorities uncovered the longest drug smuggling tunnel ever to be found on the US-Mexican border, US officials announced on Wednesday.

The tunnel stretches more than 1,313 meters (4,309 feet) — starting in an industrial area in the Mexican town of Tijuana and ending near a warehouse area in the US city of San Diego.

It comes equipped with a rail cart system, elevator, high voltage electrical cables, ventilation and a drainage system, according to a statement from US Customs and Border Protection.

Read more: Mexico: When drug violence 'turns into terrorism'

Mexican authorities discovered the "high-level narco-tunnel" last August, although the discovery was only revealed now.

"The sophistication of this tunnel demonstrates the determination and monetary resources of the cartels," said John Callery, the special agent in charge of the US Drug Enforcement Agency.

Running under the border wall

Although cross-border tunnels are not new along the US-Mexico border, the size of the tunnel and its technical components surprised authorities.

"We never really thought they had the moxie to go that far," said Lance LeNoir, a Border Patrol operations supervisor. "They continue to surprise me.''

US President Donald Trump has long pushed for an expanded border wall with Mexico, although the latest tunnel discovery shows the limitations of his plans.

The tunnel runs 70 feet (21 meters) below the surface — far below the current underground limit of the border wall. The passageway also measures around 5.5 feet tall and 2 feet wide.

The discovery has not yet led to any arrests or drug seizures. Although officials did not say who they believe is behind the tunnel, the area where it originated in Mexico is a stronghold of the Sinaloa cartel.

Under US law, authorities must now fill the US side of the tunnel with concrete to seal it off.

rs/se (AP, dpa)

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