Hyperloop is one of Elon Musk's envelope-pushing ventures, along with SpaceX and Tesla Motors

Elon Musk's Hyperloop ultra high-speed transport system will be unveiled in Los Angeles in early December with free test rides to the public, the entrepreneur announced.

"The first tunnel is almost done," Musk said on Twitter late Sunday night. "Opens Dec 10."

Responding to comments on Twitter, Musk said there would be an opening event that night and "free rides for the public next day."

Musk's venture, "The Boring Company," has been pushing the underground system as a futuristic concept that could radically speed transport within and between cities.

In another tweeted response, Musk said the test tunnel has a top speed of 155 miles per hour (250 kilometers).

Supporters of the technology have discussed a vision where a trip between Los Angeles might take 30 minutes instead of five or six hours.

A hyperloop is a shuttle that travels on magnetic rails, somewhat like a train, but which runs in a tube with little or no air. In theory, hyperloops could allow travel faster than the speed of sound.

In a presentation in Los Angeles in May, Musk said vehicles could reach downtown LA from its international airport in under 10 minutes, with a long-term objective of reaching over 300 miles an hour.

Hyperloop is one of Musk's envelope-pushing ventures, along with SpaceX and Tesla Motors. Shares of Tesla have fallen more than 30 percent since August 7, when he infamously tweeted that he had funding lined up to take Tesla private.

He subsequently paid a $20 million fine to settle after the US Securities and Exchange Commission accused the entrepreneur of fraud.

Another visionary entrepreneur, Richard Branson, who like Musk also is involved in space travel, is backing a Virgin Hyperloop One which has been testing in Nevada and opened a research center in southern Spain.

And Canadian company Transpod is working to begin testing the system in France.