A new virus belonging to the same family as the SARS virus that killed 800 people in 2002 has been identified in Britain in a man who had recently been in Saudi Arabia, the World Health Organization (WHO) said on Sunday.

The United Nations health body, which issued a statement through its "global alert and response" system, said tests on the patient, a 49-year-old Qatari man, confirmed the presence of a new, or novel, coronavirus.

Coronaviruses are a large family of viruses which includes the common cold and SARS.

"Given that this is a novel coronavirus, WHO is currently in the process of obtaining further information to determine the public health implications," the statement said.

SARS, or Severe Acute Respiratory Syndrome, appeared in China in 2002 and killed some 800 people globally before being brought under control.

Peter Openshaw, director of the Centre for Respiratory Infection at Imperial College London, said at this stage the novel virus looked unlikely to prove a concern, and may well only have been identified due to sophisticated testing techniques.

"For now, I would be watchful but not immediately concerned," he told Reuters.

The WHO said the Qatari patient had first presented to doctors on September 3, 2012 with symptoms of an acute respiratory infection.

On September 7, he was admitted to an intensive care unit in Doha, Qatar, and on September 11, he was transferred to Britain by air ambulance from Qatar.

"The Health Protection Agency of the UK conducted laboratory testing and has confirmed the presence of a novel coronavirus," the WHO said.

It said scientists at the HPA compared gene sequences of the virus from the Qatari patient with samples of virus sequenced by Dutch scientists from lung tissue of a fatal case earlier this year in a 60-year-old Saudi national.

The two were almost identical, it said.

Openshaw said the fact the two cases found so far are apparently unrelated suggests "that what has been picked up is just some rare event that in past times might have been undiagnosed".

But he added: "Any evidence of sustained human-to-human transmission or of contact would be more worrying, raising the worry that another SARS-like agent could be emerging."

The WHO said it was not recommending any travel restrictions but would be seeking further information on the virus.