A US company, backed by film director James Cameron and Google's top executives, has unveiled bold plans to mine asteroids for precious minerals and water.

Heralding a new frontier in space exploitation, Planetary Resources announced plans to send a swarm of robot miners into space to prospect resource-rich chunks of rock not far from Earth.

The firm's co-founder Peter Diamandis said he wanted to "make the resources of space available to humanity", and add trillions of dollars to global wealth in the process.

Among the goodies to be found on near-Earth asteroids are much-sought-after platinum, iron, nickel and sulfur as well as more obscure minerals that make excellent semi-conductors.

The equipment could also harvest water, which scientists believe holds the key to building propellants that will allow deep space exploration.

The first step will be to send a telescope into space within the next 18 to 24 months that can spot which asteroids may be useful.

Admitting the project was "difficult", Diamandis and his colleagues tried to silence claims that it was a flight of fantasy, assembling a veritable fantasy team of investors.

They include Google executives Larry Page and Eric Schmidt and Titanic filmmaker Cameron, as well as the son of one-time presidential candidate Ross Perot.

Cameron has a long-standing interest in exploration and recently carried out a solo submarine dive to the bottom of the Mariana Trench, the deepest part of the Pacific Ocean.

It is not the first time humans dream about taping resources beyond the bounds of Earth.

A range of visionaries from Soviet rocket scientist Konstantin Tsiolkovsky, who considered the idea in 1903 book about space exploration, to makers of the 2009 film Moon have imagined such a future.

NASA has even studied whether it would be feasible to capture a small asteroid, although there are fears such technology could be weaponised.

Scientists at the Keck Institute for Space Studies have since judged it feasible to drag a more sizeable asteroid to high lunar orbit for harvesting, but at a cost of around $US2.7 billion ($A2.63 billion).

Former NASA astronaut Tom Jones, an adviser to the startup, said the firm was trying to develop a "cost-effective, production-line spacecraft that will visit near-Earth asteroids in rapid succession".

A single 500-metre platinum-rich asteroid contains the equivalent of all the platinum group metals mined in history, according to the firm.

More than 1500 of the approximately 9000 known near-Earth asteroids are as reachable as the moon in terms of how much energy it would take for the trip.

"Our mission is not only to expand the world's resource base," said Planetary Resources chief engineer Chris Lewicki.

"We want to increase people's access to, and understanding of, our planet and solar system by developing capable and cost-efficient systems."

But outside experts like Jeffrey Kargel of the University of Arizona warn the project, while exciting, is "enormously difficult".

Kargel said the first step, launching a space telescope makes sense and could be done with relative ease, but mining a returning the minerals to Earth will be a formidable challenge.

"It's not a three-year profit line," he told AFP.

But the long-term benefits could be enormous, he added.

He likened a low-yield haul to finding a treasure-laden shipwreck at the bottom of the ocean: beneficial to the company, but not much else.

But Kargel said bringing larger quantities of minerals back to Earth could completely transform the global economy.

"It would be a what economists call a disruptive technology, suddenly some metals could become very cheap, meaning they people could consider using them in ways they never would have before because of the cost.

"That is when I really get excited."

Planetary Resources executives admit that there is a long, and as yet unpaved, road to travel.

"There will be times when we fail. There will be times when we have to pick up the pieces and try again," said co-founder Eric Anderson.

- AFP