The picture shows the prototype tunnel’s paneled walls, cables, and what appears to be a track running along the floor. The image also features a large upper conduit that snakes around the bend of a tunnel he believes will one day help alleviate urban traffic congestion.

Writing on Twitter, Musk revealed the tunnel is now around 500ft (150 meters) long and said that he had hopes that it would span the length of the north-south Interstate 405 highway by next year.

“Should be 2 miles long in three or four months and hopefully stretch the whole 405 N-S corridor from LAX to the 101 in a year so,” he said.

Musk had been digging under the SpaceX headquarters in California, but the LA tunnel is the first of the tech entrepreneur's Boring Company civil pilot projects.

READ MORE: Richard Branson gets onboard Hyperloop One

The firm also recently received provisional approval to start digging in Maryland. It is hoped that the second test dig will one day form part of an underground Hyperloop network linking Baltimore with Washington DC and New York.

Maryland Governor Larry Hogan tweeted his support for the project earlier this month.

In April, Musk released a video showing a multi-layered network of tunnels through which vehicles and pods could travel at speeds of up to 700 kilometers per hour.

Earlier this month, Richard Branson announced that his Virgin Group has bought an unspecified stake in Hyperloop One, the LA-based company developing super-fast pods for the transportation system.