Immigration and Customs Enforcement spokeswoman Lauren Mack said Thursday that the approximately 220-yard passage was lit and ventilated. It began under a bathroom sink inside a warehouse and did not cross the border into San Diego.
Mack says the Mexican army entered the tunnel Wednesday. No drugs were found and there are no arrests reported.
It is the second major tunnel discovered in less than a week along the U.S.-Mexico border. A 240-yard completed passage was discovered near Yuma, Ariz. U.S. authorities say the Arizona tunnel was operational.