Internationally-renowned mathematician Stephen Hawking, 67, was rushed to hospital Monday, said Cambridge University's head of communications Gregory Hayman.
Hawking had been suffering from a chest infection for several weeks. He was taken to Addenbrooke Hospital in Cambridge and was initially said to be seriously ill, the Associated Press reported.
Later on Monday afternoon, Hayman said Hawking was "now comfortable but will be kept in hospital overnight."
Hawking, who gained renown for his work on black holes, was 21 when he was diagnosed with the incurable degenerative disorder amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease.
Only 5 percent of people diagnosed with ALS survive for 10 years or longer, said Brian Dickie, director of research at the Motor Neurone Disease Association, the AP reported.