Physicist Stephen Hawking is "very ill" in hospital, his employers have said.

Professor Hawking, 67, who is based at Cambridge University, was said to be undergoing tests after being picked up by ambulance on Monday.

A university spokesman said Prof Hawking, who suffers from motor neurone disease, would spend the night at Addenbrooke's Hospital, Cambridge, and was "comfortable".

"Prof Hawking is very ill. He is undergoing tests," said the spokesman. "He is in a comfortable condition and will spend the night in hospital."

The spokesman said Prof Hawking, best known for his book A Brief History of Time, had been "unwell" for several weeks.

Prof Hawking - a grandfather and father-of-three, who lives in Cambridge - is wheelchair-bound and 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.

Prof Hawking has worked at Cambridge's Department of Applied Mathematics and Theoretical Physics for more than 30 years, and since 1979 has been the university's Lucasian Professor of Mathematics.

Department head Peter Haynes said Prof Hawking was a "remarkable colleague" and added: "We all hope he will be among us again soon."

Prof Hawking was born in Oxford and grew up in St Albans, Herts. He studied at Oxford University before moving to Cambridge to carry out research in cosmology. He was awarded the CBE in 1982, made a Companion of Honour in 1989 and is a Fellow of The Royal Society