Professor Stephen Hawking, one of the world's most famous scientists, is "very ill" in hospital, Cambridge University has said.
Professor Stephen Hawking is being treated in hospital
The physicist, who works at the university, has been having tests after being taken by ambulance to Addenbrooke's Hospital, Cambridge.
A university spokesman said: "Professor Hawking is very ill. He is undergoing tests. He has been unwell for a couple of weeks."
Professor Peter Haynes, head of the University's Department of Applied Mathematics and Theoretical Physics, added: "Professor Hawking is a remarkable colleague.
"We all hope he will be amongst us again soon."
One of the last times the 67-year-old scientist appeared in public was in September when he unveiled a £1m clock erected at Corpus Christi College, Cambridge.
The professor is best known for his book A Brief History of Time.
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He has motor neurone disease and is wheelchair bound. He speaks with the help of a voice synthesiser.
He developed symptoms of the disease while studying in the 1960s and is one of the world's longest surviving sufferers.
The physicist has worked at Cambridge's Department of Applied Mathematics and Theoretical Physics for more than 30 years and since 1979, he has been the University's Lucasian Professor of Mathematics.
In 1982 he was awarded a CBE and he became a Companion of Honour in 1989. In addition, he is a Fellow of the Royal Society.
After growing up in St Albans, Hertfordshire, he read physics at University College Oxford and then moved to Cambridge to carry out research in cosmology.
Prof Hawking currently lives in Cambridge and has three children and one grandchild.
Stephen Hawking. Scientist Stephen Hawking, 67, has been taken to a hospital in an ambulance after falling very ill, reports .

According to a physicist at  in the United Kingdom, "Professor Hawking is very ill" and had been rushed to  in  to undergo tests.

His condition is not yet known, but according to the University, Hawking has been ill with a chest infection for a few weeks. On April 6, he cancelled an appearance at  due to his illness. Hawking also suffers from severe .

"He Hawking is undergoing tests. He has been unwell for a couple of weeks," said the university in a statement. In a later statement, the University stated that Hawking was resting comfortably "but will be kept in hospital overnight" for observation.

 head Peter Haynes offered his sympathy saying, "Professor Hawking is a remarkable colleague. We all hope he will be amongst us again soon." Hawking has worked in the same department as Haynes for over 30 years.