SAN DIEGO — A major drug tunnel has been discovered under the San Diego-Tijuana border, a roughly 1,800-foot passageway discovered in a warehouse in Otay Mesa where U.S. authorities seized more than 20 tons of marijuana, according to U.S. and Mexican officials.

In Mexico, army troops raided a warehouse in an industrial area that concealed the tunnel entrance and seized four more tons of dope.

The back-to-back raids occurred Monday night and Tuesday morning in a light industrial area with a long history of tunnel activity.

The passageway, equipped with lighting, ventilation and a rail system, is one of the few unearthed in recent years that appears to have been fully operational.

About 75 tunnels along the U.S-Mexico border have been unearthed in the last four years, most of them in various states of construction. The discovery comes two weeks after the Mexican military in Tijuana seized a record 134 tons of marijuana.

That dope was seized in a nearby area of eastern Tijuana, but it’s not clear if the two incidents are connected.

The Mexican military said no one had been arrested on the Mexican side. It’s not clear if arrests were made in San Diego.