Three men have been arrested after the discovery of one of the most sophisticated tunnels for smuggling drugs from Mexico to the US.

With lighting, ventilation and an electric rail system, US authorities are calling the underground passage a “super tunnel” – the fifth one they have found since 2010.

More than half a kilometre of secret subway linked Tijuana in Mexico and the American city of San Diego, where the exit was inside a warehouse.

The three men in custody are said to be drivers and have been charged with possession and intent to distribute drugs.

Almost nine million euros worth of marijuana and cocaine were found inside the tunnel, which was closed down before any drugs made it onto the street.

San Diego is a popular choice for underground passages because the clay soil is easy to dig.