The human race must start leaving Earth within 30 years to avoid being wiped out by over-population and climate change, Professor Stephen Hawking has warned.

Making an impassioned speech at the Starmus science festival in Trondheim, Norway, the astrophysicist said it was crucial to establish colonies on Mars and the Moon, and take a Noah's Ark of plants, animals, fungi and insects, to start creating a new world.

Prof Hawking said it was only a matter of time before the Earth as we know it is destroyed by an asteroid strike, soaring temperatures or over-population.

He said that becoming a 'cosmic sloth' was not an option because 'the threats are too big and too numerous.'

"I am convinced that humans need to leave earth. The Earth is becoming too small for us, our physical resources are being drained at an alarming rate."

"We have given our planet the disastrous gift of climate change, rising temperatures, the reducing of polar ice caps , deforestation and decimation of animal species.

"When we have reached similar crisis in or history there has usually been somewhere else to colonise. Columbus did it in 1492 when he discovered the new world. But now there is no new world. No Eutopia around the corner. We are running out of space and the only places to go to are other worlds."