Federal authorities in San Diego have made one of the largest marijuana seizures in the United States, confiscating more than 20 tonnes of pot that was smuggled into the country through an underground tunnel connecting warehouses on either side of California's border with Mexico.
Mexican authorities seized more than four tonnes of marijuana from the warehouse on their side of the border.
The marijuana is worth more than $20 million (£12.4 million) if sold on the streets of San Diego, said US Immigration and Customs Enforcement (ICE) Director John Morton. The bricks of pot were packaged for sale.
"This is obviously the work of a cartel," said Morton, who held a news conference outside the warehouse in an industrial park near the Otay Mesa truck crossing, across from Tijuana.
Officials said the 12-hour operation started Tuesday night when US authorities watching a warehouse under surveillance followed an articulated lorry as it left the building.
ICE agents called in the California Highway Patrol, whose officers stopped the rig near Temecula, California, about 60 miles (100 kilometres) away.
Authorities say they found 10 tonnes of marijuana inside the lorry. The driver, a US citizen, and his Mexican wife were arrested.
Authorities quickly obtained a federal search warrant to enter the warehouse, where they discovered 10 to 15 more tonnes of marijuana, Morton said.
They also found the opening to the tunnel, which ran the length of six football fields under the border and ended at a warehouse in Mexico. The tunnel had lighting, ventilation and a rail system to send loads of illegal drugs into California.
Officials said the seizure was the largest ever in California and was believed to be the second-largest in the US. The largest amount of marijuana seized by Drug Enforcement Administration agents was in 2008 in Oregon, where 33 tonnes were found, DEA special agent Ralph W Partridge said.