The Border Patrol says it discovered a secret tunnel that may have been used to smuggle migrants from Tijuana, Mexico, to San Diego.
The agency said Monday that agents found the tunnel about 110 feet north of the Mexican border, east of San Diego's Otay Mesa border crossing. It measures 3 square feet and is reinforced by wood.
The Border Patrol says the tunnel began inside San Diego's vast underground storm drain system. It was unclear where it ended or if it crossed into Mexico.
Agency spokesman Mark Endicott says authorities suspect it connected to a natural gas pipeline that runs into Mexico. The pipeline is no longer used for gas.
Authorities have discovered dozens of cross-border tunnels in recent years, many of them incomplete. U.S. authorities typically destroy the tunnels.
