Image copyright SPACEX Image caption Artwork: The BFR would assume the roles performed by current SpaceX vehicles

People will soon be able to fly from city to city within minutes, rocket and car entrepreneur Elon Musk says.

Mr Musk made the promise at the International Astronautical Congress (IAC) in Adelaide, Australia.

A promotional video says the London-New York journey would take 29 minutes.

Mr Musk told the audience he aimed to start sending people to Mars in 2024. His SpaceX company would begin building the necessary ships to support the mission next year.

He says he is refocusing SpaceX to work on just one type of vehicle - known as the BFR - which could do all of the firm's current work and interplanetary travel.

Image copyright IAC Image caption Elon Musk: "That's not a typo"

Mr Musk first laid out his Mars travel ambitions at the IAC in 2016. Twelve months on, he returned with more detail.

His BFR, although still massive, is now a little smaller at 106m in height and 9m in width.

The major difference compared with the original version, however, was cost, the South African-born American said.

"I think we've figured out how to pay for it. This is very important."

The route to affordability, he explained, was in refocusing all of the company's efforts into the one system - and then using that to meet all its customers' needs.

Image copyright SPACEX Image caption Artwork: The BFR would launch much bigger or many more satellites than current rockets

This means the BFR would launch satellites and service the space station - as SpaceX's Falcon 9 and Dragon capsule do now - but also take people to the Moon and Mars, and do what is termed "point to point" travel on Earth.

"Most of what people consider to be long-distance trips could be completed in less than half-an-hour," he told the Adelaide audience.

"Some of our customers are conservative and they want to see the BFR fly several times before they're comfortable launching [on it]," Mr Musk said.

"So what we plan to do is to build ahead and have a stock of Falcon 9 and Dragon vehicles, so that customers can be comfortable if they want to use the old rocket, the old spacecraft - they can do that because we'll have a bunch in stock.

"But all of our resources will then turn to building BFR."

Image copyright SPACEX Image caption Artwork: Musk envisages colonies on Mars

As well as being the CEO and chief designer at SpaceX, Mr Musk also founded the Tesla electric car company and is chairman of SolarCity which specialises in renewables technologies, such as high-storage batteries.

He has attracted a rock-star following from fans who love his visionary thinking. And although his promises have often taken much longer to deliver, he has achieved a number of notable firsts.

These include 16-in-a-row successful landings of orbital-class rockets back on Earth after they have completed their missions. Two of these rockets have even flown a second time.

Media playback is unsupported on your device Media caption Elon Musk's 'underground road plan'

Key to his thinking is the concept of reusability. Space activity is currently expensive only because it is disposable, he says. There is no reason, he claims, why rocket systems cannot be made to operate like airliners where the most significant ongoing cost is the fuel in the tanks.

His Falcon 9 rocket is partially reusable; the BFR would be totally reusable. The same vehicle would fly time and time again.

Mr Musk recognises that his ambitious timelines sometimes slip. When he put up a slide in Adelaide stating that the first cargo (no humans aboard) versions of BFR would go to Mars in 2022, he said: "That's not a typo, although it is aspirational."

Image copyright SPACEX Image caption Artwork: Why haven't we got a lunar base yet, Musk complained

His many fans in the audience lapped up the presentation, but his numerous business customers will also have stiffened slightly at the news that SpaceX is to begin diverting its energies towards the all-new rocket system.

These customers are extremely conservative - as Mr Musk himself concedes. They are only just beginning to grapple with the idea that they can put their very expensive satellites on "second-hand" Falcons. Now they must also get used to the idea that the Falcon will eventually be replaced by another rocket system - the BFR.

Prof Alan Duffy is from the centre for astrophysics and supercomputing at Swinburne University of Technology in Melbourne.

He was among the 4,000-strong audience at the IAC.

"This is SpaceX's Elon Musk. This is what he does," he told the BBC.

"What I love about SpaceX - and why the world's scientists and engineers are willing to give them that credence - is that they make things profitable at every step of the way.

"They have a big vision, they work towards it, but the steps they take are always with the profit in mind. And if there's a profit there, you can guarantee that businesses will see it through."

Image copyright AFP Image caption Elon Musk has hinted that BFR stands for "Big F****** Rocket"

Image copyright SPACEX Image caption He has set out timelines that are aggressive even for him

Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos