A U.S. Immigration and Customs Enforcement (ICE) agent walks in a tunnel which authorities found Nov. 25, and say was used to carry drugs into the United States to an Otay Mesa warehouse Thursday, Dec. 2, in San Diego, Calif. U.S. Immigration and Customs Enforcement (ICE) agents are seeking help from Otay Mesa warehouse owners and tenants after the discovery of two major cross-border drug tunnels last month that resulted in seizueres of about 50 tons of marijuana.

An ICE agent looks into the entrance of a tunnel Thursday, Dec. 2, in San Diego, Calif., which authorities found Nov. 25, and say was used to carry drugs into the United States. At right are bags of dirt from the tunnel.

A member of the Mexican Army guards the tunnel discovered by Mexican and U.S. authorities, the second found this month, in Tijuana, Mexico, Nov. 26. The tunnel goes from a house in Tijuana to a store in the industrial area in Otay Mesa, Calif., and is about 800 meters long, according to first reports.

An ICE agent stands guard in front of blocks of marijuana in an industrial building near the Mexican border in Otay Mesa, Calif.. U.S. border police have found a sophisticated smuggler's tunnel the length of six football fields linking Southern California with Mexico and believed to have been used by drug traffickers.