A new virus from the same family as the deadly SARS disease has spread beyond China's borders for the first time with a case emerging in Thailand yesterday, UN and Thai officials said.

Thai doctors diagnosed a Chinese traveller with mild pneumonia on 8 January which was later confirmed to have been caused by the so-called novel corona virus - which has already given rise to 41 pneumonia-like cases and one death in China.

The outbreak has caused alarm because of the link with SARS (Sudden Acute Respiratory Syndrome), which killed 349 people in mainland China and another 299 in Hong Kong in 2002-2003.

The World Health Organization (WHO) confirmed that the outbreak in the city of Wuhan was caused by a previously unknown type of corona virus, a broad family ranging from the common cold to more serious illnesses like SARS.

"Laboratory testing subsequently confirmed that the novel corona virus was the cause," WHO spokesman Tarik Jasarevic said, referring to the case in Thailand.

Today, the WHO said there may have been limited human-to-human transmission of the new virus in China within families, and it is possible there could be a wider outbreak.

"From the information that we have it is possible that there is limited human-to-human transmission, potentially among families, but it is very clear right now that we have no sustained human-to-human transmission," said Maria Van Kerkhove, acting head of WHO's emerging diseases unit.

The WHO is however preparing for the possibility that there could be a wider outbreak, she told a Geneva news briefing. "It is still early days, we don't have a clear clinical picture."

Some types of the virus cause less serious diseases, while others are far more severe.

The UN agency has given guidance to hospitals worldwide about infection control in case the new virus spreads.

There is no specific treatment for the new virus, but anti-virals are being considered and could be "re-purposed", Ms Van Kerkhove said.