Billionaire entrepreneur Elon Musk's Thursday morning Tweet about getting "verbal govt approval...to build an underground NY-Phil-Balt-DC Hyperloop. NY-DC in 29 mins" sent the Internet into a tizzy. The only thing: Local governments had no idea what he was talking about.

Eric Phillips, a spokesperson for NYC Mayor Bill de Blasio, said on Twitter, "This is news to City Hall," adding that "The entirety of what we know about this proposal is what's in Mr. Musk's Tweet. That is not how we evaluate projects of any scale."

D.C. Mayor Muriel Bowser's spokesperson told DCist, "This is the first we heard of it. But we can't wait to hear more."

Musk, who has been touting his plans for the high-speed rail option for years, followed up his Tweets with, "If you want this to happen fast, please let your local & federal elected representatives know. Makes a big difference if they hear from you." Then, he admitted Friday morning, "Verbal approval was at Federal level. Still a lot of work before formal, written approval, but this opens door for state & city discussions."

Indeed: A White House spokesperson said, "We have had promising conversations to date, are committed to transformative infrastructure projects, and believe our greatest solutions have often come from the ingenuity and drive of the private sectors."

The Wall Street Journal reports, "Mr. Musk’s tweets raised more questions than they answered."

Depending on the route, such a project could require approvals from five or six state governments, said Lynne Kiesling, associate director of Purdue University’s Research Center in Economics. Ms. Kiesling’s research includes the effect of regulatory institutions on technological change.

“Stringing together five or six such approvals would be a long, costly and fractious process,” she said.

Responding to Musk's entreaty to Twitter followers, Phillips, de Blasio's spokesperson, tweeted, "also, if you're stopping by City Hall, please bring a copy of the proposal. That would help."