A photo shows a tunnel between Tijuana, Mexico, and Otay Mesa, California. AFP

Power, air conditioning and railway service: such are the amenities of a sophisticated tunnel the length of five football fields, used to smuggle cocaine from Mexico into the United States, said officials who made the shock discovery.

Federal authorities in California discovered the underground passageway last Friday as part of an investigation that led to the arrest and charging of six people, according to a Department of Justice criminal complaint.

Stretching from Tijuana, Mexico to a warehouse in Otay Mesa, south of San Diego, it is thought to be 1,744 feet (530 meters) long, 61 feet deep and four feet in diameter, the US Attorney's Office for the Southern District of California said in a statement Monday.

Underground, officials found "reinforced walls, a rail system, electricity and a ventilation system."

Six people were charged with conspiring to distribute 1,762 pounds (800 kilograms) of cocaine, and officials also seized 164 pounds of methamphetamine and 3.5 pounds of heroin.

US Department of Homeland Security agents conducting surveillance on a suburban San Diego home tracked suspects to a stash location some 300 feet from the border. While inspecting the building, the agents discovered the tunnel access point, dug right out of the cement floor.

"There is no more light at the end of this narco-tunnel," US Attorney Randy Grossman said in a the statement.

"We will take down every subterranean smuggling route we find to keep illicit drugs from reaching our streets and destroying our families and communities."

Cross-border tunnels are frequently used by traffickers who smuggle migrants lured by the "American dream," or drugs, into the United States, the world's largest consumer of South American cocaine.

According to US figures, more than 90 tunnels have been discovered in southern California alone since 1993, including another "sophisticated" underground passageway located in March 2020.

Agencies