A previously unknown respiratory illness similar to the SARS virus that spread globally has been identified in a man critically ill in Britain.
A 49-year-old man from the Gulf state of Qatar is being treated in hospital in London after picking up the virus in the Middle East.
The World Health Organisation put out a global alert on Sunday saying the virus had infected the man who had recently travelled to Saudi Arabia - where another man with an almost identical virus had already died.
The UN organisation has not recommended any travel restrictions.
Britain's Health Protection Agency said it was recommending the Qatari patient be treated in isolation by doctors and nurses wearing gowns, gloves respirators, goggles and other protective equipment.
It did not recommend any specific actions for travellers or other members of the public.
The virus, known as a coronavirus, comes from the same family as SARS which emerged in 2002 and killed 800 people.
Coronaviruses are a large family of viruses that includes causes of the common cold but can also include more severe illness.
A British virologist says there is no evidence of a link between the two cases.
Andrew Easton, of the University of Warwick, says how or if the virus can be transferred is not yet known, and people should not be alarmed at this stage.