Drug cartels have built hundreds of tunnels to move drugs into California.
But it's unusual to find such a large group of foreigners, especially from as far away as China, come out of an illegal border tunnel, Border Patrol agent Eduardo Olmos said.
Agents detained 23 Chinese nationals and seven Mexicans. "To say the least, this is definitely a significant event because of the amount of people," Olmos said.
When agents headed towards them, the migrants ran toward a hole in the ground near a border fence. The hole was covered with a few branches and a wooden ladder led down to an underground passageway to Mexico.
More From This Section
Olmos said he did not know the tunnel's length or dimensions. Agents captured 30 migrants, he said, but he did not know how many of those detained were grabbed while getting into the hole or whether any of them made it back into the tunnel and returned to Mexico.
Many tunnels found by agents in San Diego have had lighting, ventilation and even railroad-type tracks so the drug cartels could efficiently move their loads into California. In Arizona, smugglers used to move migrants through storm drainage pipes that lie under the US-Mexico border.
Smugglers in San Diego occasionally moved a few people through narrow, quickly excavated tunnels that authorities call "gopher holes."
It was unclear how long the newest tunnel found had been there and how many may people have used it, but officials said it may have been built as an extension of a previously discovered incomplete tunnel found by Mexican authorities.
Smugglers also wanted to avoid having their cargo the people they were moving expose their routes, like they did on Saturday.
But the event may indicate it has become profitable enough for them do so because Chinese nationals can pay up to USD 20,000 a person to be brought from their homeland to the United States, Unzueta said.
"You're making a higher profit margin with Chinese nationals versus Mexican nationals," Unzueta said.
They are being held at a detention center while authorities review their cases, Olmos said. It was not known if a smuggler was among those detained.
US authorities plan to seal the tunnel with cement but will first map it to determine its path between the countries.