Inside a drug smuggling tunnel on the US-Mexico border

The US authorities have discovered 20 tonnes of marijuana, worth tens of millions of dollars, in one of the most advanced illegal tunnels ever found.

The passage is half a mile long and runs from inside a house in Mexico straight under the border with the United States and into a warehouse in San Diego.

The tunnel had its own lighting, ventilation and a system of tracks and trolleys for transporting drugs.

The BBC's Rajesh Mirchandani has been shown around.