11/17/11 4:20 Break

SAN DIEGO (AP) — An estimated 14 tons of marijuana was seized after the discovery of a tunnel that the authorities said on Wednesday was one of the most significant drug smuggling passages ever found on the United States-Mexico border.

The tunnel stretched about 400 yards and linked warehouses in San Diego and Tijuana, Mexico, the authorities said.

The authorities in the United States seized 9 to 10 tons of marijuana on Tuesday inside a truck and at the warehouse in San Diego’s Otay Mesa area, said Derek Benner, Immigration and Customs Enforcement’s special agent in charge of investigations in San Diego. Mexican authorities recovered about five tons.

Photos taken by the Mexican authorities show an entry blocked by bundles that were most likely stuffed with marijuana, said Paul Beeson, chief of the Border Patrol’s San Diego sector. Wooden supports lined the walls, and power cords led to the Mexican entrance, suggesting lighting and ventilation systems.

The depth and the width of the tunnel were unknown. Several arrests were made. Mr. Benner declined to give details.

As the United States intensifies enforcement on land, more than 70 tunnels have been found on the border since October 2008, surpassing the number of discoveries in the previous six years.

Many are clustered in San Diego, California’s Imperial Valley and Nogales, Ariz. California is popular because its claylike soil is easy to dig. In Nogales, smugglers tap into vast underground drainage canals.

Raids last November on two tunnels linking San Diego and Tijuana netted a combined 50 tons of marijuana on both sides of the border, two of the largest such seizures in United States history. Those secret passages were lined with rail tracks, lighting and ventilation.

A version of this article appeared in print on November 17, 2011, on page A21 of the New York edition with the headline: 14 Tons of Marijuana Seized After Border Tunnel Found.