Elon Musk promises NY-DC run in 29 mins

US entrepreneur Elon Musk said Thursday he'd received tentative approval from the government to build a conceptual "hyperloop" system that would blast passenger pods down vacuum-sealed tubes from New York to Washington at near supersonic speeds.

"Just received verbal govt approval for The Boring Company to build an underground NY-Phil-Balt-DC Hyperloop. NY-DC in 29 mins," the flamboyant CEO of Tesla and SpaceX tweeted, using abbreviations for New York, Philadelphia, Baltimore and Washington DC.

New York and Washington are separated by some 330 kilometers (200 miles) -- currently an approximately three-hour journey by train or one hour and 15 minutes flying.

The US Department of Transportation forwarded queries for comment to the White House, which offered a statement that neither confirmed nor outright dismissed the bombastic announcement.

"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 sector," the statement said.

Experts however said the proposed system would likely require approvals from numerous departments as well as local and state authorities before construction work could begin.

Facing a barrage of skepticism, Musk, who has been known to over-promise in his announcements, clarified: "Still a lot of work needed to receive formal approval, but am optimistic that will occur rapidly," urging people to lobby their representatives.

Musk's involvement in the proposed project is for now limited to building the tunnels, and it is not yet clear which firm he plans to partner with to handle the pod vehicles.

But several companies are now exploring the market, including Northeast Maglev, Hyperloop One and Hyperloop Transportation Technologies.

Beyond the Hyperloop system, Musk has made plans to send two private citizens around the Moon and land an unmanned spacecraft on Mars by 2020.

Earlier this month he vowed to build the world's largest battery in Australia with a 100 megawatt-hour capacity, or enough to power 30,000 homes.