Entrepreneur Elon Musk says he's received "verbal government approval" to build an underground transport hyperloop between New York and Washington DC, although he did not say who gave the approval or how any such project would proceed.
Mr Musk, the outspoken chief executive of electric car maker Tesla Inc and rocket company SpaceX, advocates developing magnetically levitated hyperloop trains that would travel in airless tunnels, which he says would be more efficient and faster than current high-speed trains.
He recently started a project, the Boring Co, to build transport tunnels.
In two tweets on Thursday he said, "just received verbal government approval for the Boring Company to build an underground NY-Phil-Balt-DC hyperloop. NY-DC in 29 mins" and that the trains would go city centre to city centre.
By travelling in vacuum tubes on magnetic cushions, hyperloop trains would avoid being slowed down by air pressure or the friction of wheels on rails, making them faster and cheaper to operate, supporters say. A number of start-ups have begun to develop the technology, despite concerns about the cost and practicality.
Major infrastructure projects typically require complex approval from various levels of government and likely would cost billions of dollars.
President Donald Trump in March met with Mr Musk, who raised the Boring Company idea then, White House officials said. Mr Musk also talked about his plans to launch a mission to Mars.
White House National Economic Council Director Gary Cohn in April praised the idea of Mr Musk using tunnels to speed rail transit on the densely populated east coast of the United States and also to cut traffic congestion in Los Angeles.
The White House and Transportation Department did not immediately comment on Mr Musk's tweet. The Boring Company did not immediately respond to a request for comment.