LONDON: A British man infected with a new virus from the same family as SARS has died, health officials said on Tuesday, bringing the worldwide death toll from the previously unknown disease to six.

The virus, called novel coronavirus or NCoV, was unknown in humans until it emerged in the Middle East last year. There have been 12 confirmed cases worldwide - including in Saudi Arabia, Jordan and Britain - and so far six patients have died.

"This patient had an underlying condition that may have made them more susceptible to respiratory infections," the Health Protection Agency said in a statement announcing the death of one of four people in Britain with the NCoV infection.

NCoV was identified when the World Health Organisation issued an international alert in September 2012, saying a completely new virus had infected a Qatari man in Britain who had recently been in Saudi Arabia.

Since then 12 cases have been identified, including a cluster of cases reported last week in a family in Britain.

The HPA said it had identified and followed up more than 100 people who had close contact with the cases in this family cluster.

"Besides the identified secondary cases, all tests carried out on contacts to date have been negative for the novel coronavirus infection," it said.

Coronaviruses are a family of viruses that includes those that cause the common cold as well as the one that caused SARS - which emerged in China in 2002 and killed about a 10th of the 8,000 people it infected worldwide.