Speaking on a six-day visit to Hong Kong, Hawking said: "It is important for the human race to spread out into space for the survival of the species.

"Life on Earth is at an ever increasing risk of being wiped out by a disaster such as sudden global warming, nuclear war, a genetically engineered virus or other dangers we haven't yet thought of.

"But if we can avoid killing ourselves for the next hundred years we

should have settlements that can continue without support from Earth," he

said, predicting a lunar settlement within 20 years and a Martian colony

in 40.

Hawking, a Lucasian Professor of Mathematics at the University of Cambridge who speaks with a voice synthesiser and has been in a wheelchair since developing motor neurone disease when he was a teenager, then revealed he was writing a science book for children with his daughter.

"It will be a bit like Harry Potter in the universe, about science, no magic," Hawking told reporters.

His daughter, Lucy Hawking, a journalist who is travelling with her father, said the book would be about theoretical physics.

"It's like Harry Potter meets 'A Brief History of Time,'" she said.

'A Brief History of Time' was the international best seller written by her father. It attempted to explain a range of subjects in cosmology, including the Big Bang, black holes, light cones and superstring theory, to the nonspecialist reader.

"I have an eight-year-old son and we both see this project as a way of explaining my father's work to him," she said.

It is the 64-year-old's scientist's first visit to Hong Kong.

He will deliver a lecture on Thursday titled "The Origin of the Universe" to an audience of 2,500 at the Institute for Advanced Studies at the Hong Kong University of Science and Technology.

The university said Hawking will discuss theories on the origin of the universe and time.

During his visit, Hawking will meet with Hong Kong chief executive Donald Tsang before heading to Beijing where he will give a public lecture on string theory.

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