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Not so fast, Elon Musk.

The tech billionaire said he has received "verbal" government approval for The Boring Company — his tunnel venture — to build an underground "hyperloop" connecting New York to Washington, D.C.

The travel system would replace conventional trains with minivan-sized pods that would essentially blast through small tubes. By bringing to near vacuum levels of air pressure, there would be little aerodynamic resistance, allowing them to jet along at nearly supersonic speeds. Total travel time, Musk estimated, would be just 29 minutes, or a fraction of what it today takes even by air, never mind the fastest conventional trains operated by Amtrak.

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

Related: Hyperloop Track Unveiling Brings Elon Musk's Dream a Step Closer to Reality

Musk hasn't said who — or what agency — he received this "verbal" government approval from. Musk has reportedly maintained strong White House connections — he was a member of President Donald Trump’s economic advisory council until withdrawing in protest after the president withdraw from the Paris climate accord.

Thursday's somewhat premature statement left many people wondering. Musk later clarified: "Still a lot of work needed to receive formal approval, but am optimistic that will occur rapidly."

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A representative from The Boring Company said there have been "a number of promising conversations with local, state and federal government officials. With a few exceptions, feedback has been very positive and we have received verbal support from key government decision-makers for tunneling plans, including a Hyperloop route from New York to Washington DC. We look forward to future conversations with the cities and states along this route and we expect to secure the formal approvals necessary to break ground later this year. "

"He is a marketing genius. In many ways, it is similar to how our president uses marketing channels," Adie Tomer, fellow at Brookings Institution's Metropolitan Policy Program, told NBC News.

While Musk could be tweeting to drum up support for his idea, Tomer said the project would take years of negotiations and approvals before even breaking ground.

"You are really stretching between not only the biggest economic center in the country but also a string of metropolitan areas. There are a tremendous amount of actors to deal with," Tomer said.

City center to city center in each case, with up to a dozen or more entry/exit elevators in each city — Elon Musk (@elonmusk) July 20, 2017

Genevieve Giuliano, a transportation policy expert at the University of Southern California, told NBC News the project would first require a full environmental review.

"All state and local governments potentially affected would be participants, along with federal and state environmental agencies, safety agencies, natural resource agencies, etc.," she said. "Since this is an interstate project, either the approval process would be led by the federal government, or some sort of multi-state joint powers agency would be formed to review and provide oversight."

Musk said the plan would be "city center to city center in each case, with up to a dozen or more entry/exit elevators in each city," — which raises another question.

"There would have to be stations somewhere; the question is where, and how would the property or use rights be acquired?" Giuliano said.

Aside from the digging, regulators will also need to sign off on the hyperloop before the first human passengers get inside a pod and travel through the underground system.

"We are still not looking at a proven technology," Tomer told NBC News.

Mark Hallenbeck, director of the Washington State Transportation Center at the University of Washington, told NBC News there's also a question of which agency would oversee the hyperloop.

"Is Hyperloop an airline, a rail line or something else?" Hallenbeck asked. "Whoever gets assigned to it will have to make a determination that the system is safe, and can/should be used by the public. Don't ask me how they will make such a decision, but it won't be based on some nice simple meeting resulting in a verbal approval."

The bottom line here: Experts agree we're still a long way away from seeing any New York-to-Washington hyperloop.

"It is hard enough to get the new tunnels under New Jersey and New York we desperately need," Tomer said. "That's going to take five to 10 years to get that done, so if we are talking about a new tunneled rail line, that's a true mega project."

The world’s longest and deepest rail tunnel, the Gotthard Base Tunnel, which travels 35.5 miles under the Swiss Alps, cost the equivalent of $10 billion. Work began in November 1999, and full service didn't begin until December 2016.