Elon Musk claims to have been given government approval to build a super-fast underground hyperloop train whisking passengers from New York City to Washington DC in just 29 minutes.

The 230-mile route currently takes around four hours to drive or three hours by train. Musk says the hyperloop will go from one city centre to the other, calling at Philadelphia and Baltimore along the way.

Musk, who will build the tunnel using his new firm, The Boring Company, tweeted on 20 July to say he has "received verbal government approval" to build the underground route, which if made a reality will see trains travel at hundred of miles per hour through a tunnel with much of its air removed to reduce drag.

In a follow-up tweet, Musk added: "City centre to city centre in each case, with up to a dozen or more entry/exit elevators in each city."

Minutes later, when asked on Twitter if he would consider a route in Texas, connecting Dallas to Austin via Houston and San Antonio, Musk said: "For sure. First set of tunnels are to alleviate greater LA urban congestion. Will start NY-DC in parallel. Then probably LA-SF and a TX loop."

Musk first revealed plans for a hyperloop train via a whitepaper published online back in 2013. It explains how a train, levitating with magnets similar to the highspeed trains of Japan, can blast through a low-pressure tunnel at up to 600mph , faster than a commercial airliner.

At the time Musk said he did not have time to pursue the hyperloop, as he was busy as chief executive of electric car company Tesla and space rocket manufacturer SpaceX. Despite that still being the case, Musk is now also boss of a new firm called The Boring Company, which he hopes to use to drastically improve tunnel boring speeds.

These tunnels, Musk has said previously, will be used to ferry cars sitting on electric sleds between stations under cities, relieving the roads of congestion above. With his tweets today, it now seems like Musk wants to combine the two projects into one, boring tunnels for a hyperloop train.