The tunnel, which measures 370 feet long, connects the warehouses of an industrial park in San Diego, California and the Mexican city of Tijuana, said the U.S. administration of customs and immigration.
Last year, U.S. police discovered two smuggling tunnels equipped with lighting and ventilation between Southern California and Mexico.
The Mexican drug cartels have dug many tunnels under the border with the United States in recent years to circumvent security measures.
Most Mexican cities connect to California or Arizona. The longest tunnel found so far to early 2006 – linking Otay Mesa (south of San Diego) in Tijuana and measured 730 meters long.
Tijuana is the main starting point for Mexican drug to California next. More than 42,000 people have died in the war against the cartels launched by President Felipe Calderon on his arrival to power in 2006.