Professor Hawking is giving this year's BBC Reith Lectures, which explore research into black holes, and his warning came in answer to audience questions. He says that assuming humanity eventually establishes colonies on other worlds, it will be able to survive.
"Although the chance of a disaster to planet Earth in a given year may be quite low, it adds up over time, and becomes a near certainty in the next thousand or ten thousand years.
"By that time we should have spread out into space, and to other stars, so a disaster on Earth would not mean the end of the human race.
"However, we will not establish self-sustaining colonies in space for at least the next hundred years, so we have to be very careful in this period."
Reith Lectures: Prof Stephen HawkingProf Hawking's first Reith Lecture will be broadcast on 26 January and on 2 February at 9am on BBC Radio 4. BBC World Service listeners can tune in on 26 January at 15:06 GMT and 2 February at 15:06 GMT or catch up online via www.bbc.com/worldserviceradio
Source: BBC at http://www.bbc.co.uk/news/science-environment-35344664