U.S. Border Patrol agents in San Diego discovered a cross-border smuggling tunnel near the Otay Mesa port of entry early Saturday morning.
The tunnel was discovered after agents came across several people who had just been smuggled into San Diego.
"U.S. Agents searched the area and discovered a crude opening in the ground with a ladder inside and determined that is was a smuggling tunnel. The tunnel's exit is located just north of the secondary fence in the vicinity of the Otay Mesa port of entry," U.S. Customs and Border Protection (CBP) said in a statement.
As a result, 30 undocumented immigrants, including 23 Chinese nationals and seven Mexican nationals, were taken into custody for further questioning.
CBP said members of the San Diego Tunnel Task Force are working closely with their law enforcement counterparts in Mexico on the investigation.
"While subterranean tunnels are not a new occurrence along the California-Mexico border, they are more commonly utilized by transnational criminal organizations to smuggle narcotics," CBP noted. "However, as this case demonstrates, law enforcement has also identified instances where such tunnels were used to facilitate human smuggling."
A preliminary investigation revealed that this tunnel may be an extension of an incomplete tunnel previously discovered and seized by Mexican authorities, CBP said.