HONG KONG, 14 June 2006 - British physicist and mathematician Stephen Hawking said yesterday that the human race should reach for the stars in order to survive.

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.