A US scientist claims that machines will achieve human-level artificial intelligence within the next 21 years.

Dr Ray Kurzweil, speaking yesterday at the American Association for the Advancement of Science, described a future where machine intelligence will surpass that of the human brain as computers learn to teach and replicate among themselves.

Dr Kurzweil is one of 18 influential thinkers, along with Google founder Larry Page and genome pioneer Dr Craig Venter, chosen to identify the great technological challenges facing humanity in the 21st century by the US National Academy of Engineering.

"The paradigm shift rate is now doubling every decade, so the next half century will see 32 times more technical progress than the past half century," said Dr Kurzweil.

"Computation, communication, biological technologies such as DNA sequencing, brain scanning, knowledge of the human brain, and human knowledge in general are all accelerating at an ever-faster pace, generally doubling price-performance, capacity and bandwidth every year."

Miniaturised 3D chips with vastly improved performance made out of biological molecules will drive a merging of man and machine, thanks to devices implanted in the body to boost health and intelligence.

"3D molecular computing will provide the hardware for human-level 'strong artificial intelligence' by the 2020s," said Dr Kurzweil.

"The more important software insights will be gained in part from the reverse engineering of the human brain, a process which is well under way. Already, two dozen regions of the human brain have been modelled and simulated."