The partly self-taught AlphaGo programme's defeat of Go grandmaster Lee Se-Dol showed AI was progressing faster than widely thought, they said -- a highly symbolic moment in humanity's quest to create smart machines.

And while AI plays a key role in building a better, safer world, some fear the fast pace of development could finally leave humans outwitted by our own inventions.

AlphaGo's triumph "shows that the methods we do have are even more powerful than we first thought," said AI expert Stuart Russell of the University of California's Berkeley Electrical Engineering & Computer Sciences department.

"The fact that AI methods are progressing much faster than expected makes the question of the long-term outcome more urgent," he told AFP by email.