Billionaire entrepreneur Elon Musk is one of the project's key backers / Getty

The tunnels appear to be part of a future transportation project

Elon Musk is digging huge holes underneath America.

The PayPal and Tesla founder has finally revealed the huge tunnels he is creating as part of "The Boring Company" – a plan for a future transportation network that he has said very little about.

Mr Musk said that he hopes that the tunnels will soon be found all the way under Los Angeles. But they will initially run between the city's airport and various neighbourhoods, he suggested.

Inside the tunnel is expected to be found a "3D" transport network, that will see Mr Musk's company provide travel through the ground. That will help people overcome the problems with traffic and other transport limitations found in Los Angeles, he has said.

One video shared by Mr Musk apparently shows the beginning of the first of those tunnels, after a hole had been made to allow the vast machinery required to dig them to be placed under the ground.

In another image, Mr Musk showed those boring machines being put into the tunnel.

And perhaps most important of all, he showed a "test run of our electric sled", which appears built to carry cars at superfast speeds under the ground, so that their passengers could get back out again at the other side and continue their journey by driving.

Mr Musk originally made his fortune through payments system PayPal, but has spent large amounts of that money on transportation projects. That includes Tesla, his electric car company, as well as rocket firm SpaceX and now The Boring Company.

The idea for The Boring Company was first floated on Twitter, and many wondered whether it had been a joke. But Mr Musk has been revealing parts of the plan over time, including the new and unprecedented disclosure of how the tunnel might work.