SAN DIEGO (AP) — Authorities in California say they have found a smuggling tunnel that carried dozens of people across the border from Mexico into the United States.

Border Patrol agents discovered the crude tunnel described as a hole in the ground with a ladder inside it shortly after 1 a.m. Saturday near San Diego’s Otay Mesa border crossing.

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The San Diego Union-Tribune says agents saw a group of men and women in the street who ran when the agents approached. Some people tried to get back into the tunnel.

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Agents detained 23 Chinese nationals and seven Mexican citizens they believe crossed into the U.S. illegally.

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Authorities say the tunnel may be an extension of an incomplete tunnel previously discovered by Mexican authorities.