US officials say they have uncovered a major drug-smuggling tunnel under the border with Mexico and seized an estimated 14 tons of marijuana. Customs officials said the tunnel linked warehouses in Tijuana, Mexico, and Otay Mesa, in California. Pictures of the tunnel showed wooden supports and electric cables indicative of lighting and ventilation systems. Dozens of such tunnels have been found in recent years as US police have cracked down on overland smuggling. More than 30 have been discovered this year, Mexican authorities said, according to AFP news agency. The tunnels are also used to smuggle illegal migrants into the US. Nine or 10 tons of marijuana was found on the US side of the tunnel while Mexican police seized five tons on their end, said Derek Benner, a special agent with the US Immigration and Customs Enforcement agency. The tunnel was estimated at 400 yards (365m) in length but it was not clear how deep or wide it was. Other tunnels found by US police have included tracks, lights and ventilation systems.