Border Patrol agents apprehended 30 illegal immigrants, including nearly two dozen Chinese nationals, who entered the U.S. from Mexico through an underground tunnel near San Diego Saturday morning.

Agents uncovered the cross-border smuggling tunnel near the Otay Mesa port of entry early Saturday. Shortly after making the discovery, agents came across a large group of people who "had apparently just been smuggled into the U.S.," a U.S. Customs and Border Protection news release stated.

Border Patrol found a ladder inside the ground tunnel and concluded its northern exit was just north of the secondary fence near the port of entry.

Twenty-three of the illegal immigrants are from China, and the other seven are from Mexico.

The 30 people were taken into custody and will be questioned about how they arrived stateside since tunnels are typically used by drug cartels to smuggle products, not people.

"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. However, as this case demonstrates, law enforcement has also identified instances where such tunnels were used to facilitate human smuggling," CBP said in a statement.

The San Diego Tunnel Task Force, under the U.S. Immigration and Customs Enforcement's Homeland Security Investigations agency, was on the scene investigating the tunnel following the weekend incident.