US and Mexican police have discovered a tunnel used to smuggle drugs across the California-Mexico border and seized some 25 tonnes of marijuana.
The tunnel, equipped with ventilation, lighting and a pulley system, was 550m (1,800ft) long but just waist high.
Police said it connected a warehouse on the US side with one in Tijuana, the main gateway for drugs into California.
Mexican cartels have dug scores of border tunnels, although many of those detected had not been finished.
The latest tunnel was discovered after US agents patrolling near the border crossing in the Otay Mesa area of San Diego pulled over a tractor trailer that had left a warehouse under surveillance.
Agents found some 10 tonnes of marijuana on the vehicle, while another 10 to 15 tonnes were seized in a subsequent raid on the building. A US citizen and his Mexican wife were arrested.
"This wasn't a mom-and-pop operation, or, in this case, a husband and wife operation," said John Morton, director of the US Immigration and Customs Enforcement agency (ICE).
"This is clearly organised crime at work. This was the cartels."
At the warehouse, officers also found the entrance to the tunnel, which was just over a metre (4ft) high. The tunnel had lighting, ventilation and rails, which agents believed were used for a pulley system to ferry packets of drugs across the border.
The entrance to the tunnel on the Mexican side was found in an abandoned warehouse on the outskirts of Tijuana.
"The Mexicans moved as quickly as we did. It was an example of the co-ordination needed to be successful," said Mr Morton.
Authorities believe the tunnel had been in operation for less than a month.
Mexican soldiers confiscated some five tonnes of marijuana, a military spokesman said.
The seizures came a fortnight after Mexican authorities made a major haul of cannabis in Tijuana of some 134 tonnes.
Police say drug traffickers are building the tunnels to bypass ever more stringent controls aimed at curtailing the cross-border trade in illegal drugs and guns.
About 75 tunnels have been found in the past four years, many of them still being dug out.
In 2006, police discovered a 731m (2,400ft) tunnel, the longest found so far, also linking Otay Mesa with Tijuana.
Some 28,000 people have died in drug-related violence in Mexico since December 2006 when the government launched a crackdown on the gangs that control the routes for trafficking drugs into the US market.