• The Boring Company said it has raised $675 million in a funding round valuing the firm at $5.675 billion.
• The Elon Musk-owned venture wants to eliminate "soul-destroying traffic" with vast networks of tunnels.
• The firm says it plans to spend the fresh cash on scaling Loop, its high-speed underground tunnel project.

Elon Musk's Boring Company wants to build a network of underground tunnels to transport people and cargo around cities. It's just raised $675 million to push further toward that goal.

The Boring Company said late Wednesday that it raised the fresh funds in a Series C funding round valuing the firm at $5.675 billion.

The Boring Company says its ultimate aim is to eliminate "soul-destroying traffic" with vast networks of tunnels. The firm plans to spend the latest cash on scaling Loop, a system that will shuttle passengers through high-speed tunnels.

The start-up has previously claimed the technology could one day shuttle passengers at up to 150 miles per hour. It has so far struggled to hit those speeds, reaching a maximum of only 50 mph in test rides with reporters in a Tesla Model X electric car.

The Boring Company says it recently won approval for a 29-mile tunnel network connecting 51 stations under Las Vegas. The company is calling it the "largest subsurface transportation project," and says it will eventually be capable of transporting 57,000 passengers per hour.

It's a far cry from the "hyperloop" concept, first envisioned by Musk, which would see pods whiz through a series of underground tubes at even faster speeds — as much as 760 mph, according to one company developing the tech. Several firms are hoping to make the technology a reality.

For now, Hyperloop says it's focused on developing its Loop project and Prufrock, The Boring Company's line of machines designed to dig huge tunnel infrastructure projects in a matter of weeks.

The Boring Company says it will "significantly increase hiring across engineering, operations, and production" to build out its Vegas Loop project, and for research and development.

As if Musk didn't have enough on his plate already, the tech billionaire is also proposing a deal to buy Twitter and take the company private.

The Tesla and SpaceX CEO has offered to acquire the social media platform for $43 billion, but there are doubts over whether he can secure the required funding to make such a large bid. Twitter's board has adopted a so-called "poison pill" strategy designed to fend off a possible hostile takeover.

Tesla reported an 81% jump in first-quarter revenues Wednesday, beating analyst expectations and sending shares of the firm up more than 7% in after-hours trading.

Clarification: The photo caption in this article has been clarified to remove any impression that the Hawthorne tunnel was yet to open.