Federal law enforcement agencies have seized more than 20 tons of marijuana on the U.S. end of a smuggling tunnel in one of the largest drug seizures in the country, the Drug Enforcement Agency announced.

Agents from the San Diego Tunnel Task Force — comprised of the DEA, ICE, Border Patrol and California Bureau of Narcotic Enforcement — uncovered the crawlspace-sized tunnel running 600 yards.

Approximately 30 tons of marijuana with a street value of $20 million have been seized in the U.S. and Mexico and linked to the tunnel.

The passageway connects an Otay Mesa warehouse in the 9000 block of Via de la Amistad with a similar building in Tijuana, Mexico. The tunnel is equipped with rail, lighting and ventilation systems. Based on preliminary indications, authorities believe the passageway was probably completed recently. 

"Not only will this seizure significantly disrupt the responsible cartel by stripping from it millions in potential drug profits, but it will also keep this dangerous and addictive drug off our streets and out of our neighborhoods," according to Michele Leonhart, DEA's acting administrator.

While conducting surveillance in the Otay Mesa area on Wednesday, task force agents observed suspicious activity involving a tractor trailer truck parked at the warehouse where the tunnel entrance was later discovered. After the truck left the location, agents kept it under surveillance, alerting the Border Patrol as it approached the traffic checkpoint in Temecula.

At the traffic checkpoint, Border Patrol agents stopped the vehicle and a subsequent search of the truck's trailer revealed 10 tons of marijuana packed in large cargo boxes. The vehicle's driver and passenger were taken into custody and will be prosecuted on federal drug smuggling charges.

Following the seizure, task force agents obtained a federal search warrant for the Otay Mesa warehouse. When they entered the building Tuesday night they discovered a second cache of marijuana, weighing an estimated 15 tons, and the entrance to the cross-border tunnel.

Task force agents then alerted Mexican military personnel who located the tunnel's other entrance at a warehouse in Tijuana. Inside that building, Mexican authorities recovered another four tons of marijuana.