A new respiratory illness similar to the Sars virus that spread globally in 2003 and killed hundreds of people has been identified in a man who is being treated in Britain.
The 49-year-old man, who was transferred to a London hospital by air ambulance from Qatar, is the second person confirmed with the coronavirus.
The first case was a patient in Saudi Arabia who has since died.
Officials are still determining what threat the new virus may pose.
The World Health Organization has not recommended any travel restrictions.
Prof John Watson, head of the respiratory diseases department at the UK's Health Protection Agency, said: "In the light of the severity of the illness that has been identified in the two confirmed cases, immediate steps have been taken to ensure that people who have been in contact with the UK case have not been infected, and there is no evidence to suggest that they have.
"Further information about these cases is being developed for healthcare workers in the UK, as well as advice to help maintain increased vigilance for this virus."
He said there was no specific evidence of the virus spreading from person to person and he had no advice for the public or returning travellers.
Peter Openshaw, director of the Centre for Respiratory Infection at Imperial College London, told Reuters that at this stage the novel virus looked unlikely to prove a concern, and may well only have been identified due to sophisticated testing techniques.
And Prof John Oxford, a virology expert at Queen Mary, University of London, said he felt "somewhat relaxed" about the news.
"Sars was very quick off the mark infecting hospital staff etc and this new virus does not to me appear to be in the same 'big bang' group."
Coronaviruses are a large family of viruses which includes ones that cause the common cold and Sars (severe acute respiratory syndrome).
This new virus is different from any coronaviruses that have previously been identified in humans.
There have been a small number of other cases of serious respiratory illness in the Middle East in the past three months, one of whom was treated in the UK but has since died.
This person's illness is also being investigated, although there is no evidence as yet to suggest that it is caused by the same virus or linked to the current case. No other confirmed cases have been identified to date in the UK.
Sars is a serious respiratory infection that caused a global outbreak in 2002, spreading from Hong Kong to more than 30 different countries around the world and killing around 800 people. Although it has not been eradicated its spread was fully contained in 2003. Like other coronaviruses, it is spread through droplets of body fluids - produced by sneezing and coughing.