In a Thursday Tweet, Elon Musk says he has "verbal government approval" to build a tunnel for high-speed transportation from New York to Washington.

Just received verbal govt approval for The Boring Company to build an underground NY-Phil-Balt-DC Hyperloop. NY-DC in 29 mins. — Elon Musk (@elonmusk) July 20, 2017

The billionaire entrepreneur didn't say who gave him the approval. The "Boring Company" mentioned in his tweet refers to the fact that his Hyperoop company is boring tunnels for his super speedy trains.

Musk went on to say over social media that there was "still a lot of work needed to receive formal approval" for his plans, but that he was "optimistic that will occur rapidly."

Still a lot of work needed to receive formal approval, but am optimistic that will occur rapidly — Elon Musk (@elonmusk) July 20, 2017

But the White House said little beyond confirming it has had "promising discussions to date" and saying it is "committed to transformative infrastructure projects."

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Musk says the hyperloop could ferry people and cars from New York to Washington in 29 minutes. The system would also have stops in Philadelphia and Baltimore.

In a statement to CBS News, Ben Sarle, Deputy Press Secretary for New York City Mayor Bill de Blasio, said "nobody in City Hall, or any of our city agencies, has heard from Mr. Musk or any representatives of his company."

A representative for Philadelphia Mayor Jim Kenney's office also told CBS News that Musk has had no contact with Philadelphia officials on the matter, adding that there are "numerous hurdles" for the Hyperloop technology before it can be implemented.

Musk initially served on two White House business councils, but quit them last month after President Donald Trump announced he would withdraw the U.S. from the Paris climate accords.

CBS News' Kris Van Kleave and Marc Schwartz contributed to this story.