Underground Drug Railway Found Running from San Diego to Tijuana [VIDEO]

A sophisticated drug smuggling tunnel between the US and Mexico border which would have cost millions to construct has been discovered by officials.

The 1,760 feet (536 meters) tunnel - complete with electricity, ventilation and a fully functional rail system - connected the border towns of San Diego in California and Tijuana in Mexico.

Custom officials also seized more than eight tonnes of marijuana and 325lb (147kg) of cocaine. Three men were later arrested on suspicion of possession of marijuana and cocaine with intent to supply.

US Immigration and Customs Enforcement (ICE) spokeswoman Virginia Kice said the underground passageway was found before it could have been used.

Authorities have not revealed exactly were the tunnel is located, but it is believed to be near Tijuana airport. The tunnel zig-zaged for nearly a third of a mile at an average depth of 35ft. It is four feet in height and three feet wide.

"They've worked very hard over a year, maybe two years to build a tunnel of this sophistication. It's taken hundreds of thousands of man hours and millions of dollars to complete," said Bill Sherman of the Drugs Enforcement Administration (DEA).

The drug-tunnel is believed to have been built and operated by the Sinaloa Mexican drug cartel.

More than 75 underground passages have been discovered along the border since 2008. This latest one is the eight passage discovered in San Diego since 2006.

In November 2011, authorities found a 1,800 feet tunnel that resulted in seizures of 32 tons of marijuana on both sides of the border, one of the largest marijuana busts in US history. The tunnel was equipped with electric rail cars, lighting and ventilation and used wooden panels to line the floor.