LONDON/BEIJING: An outbreak of pneumonia that has killed one person in China and infected 40 others appears to be linked to a single seafood market in the central city of Wuhan and has not spread beyond there so far, the World Health Organization said on Sunday.

The cluster of infections had raised fears of a potential epidemic after China said last week that the virus causing it was a previously unknown type but came from the same family of viruses that caused the SARS and MERS epidemics.

However, the WHO said the outbreak had not spread. The seafood market in Wuhan - a major domestic and international transport hub - is now closed and no cases have been reported elsewhere in China or internationally, it said.

"The evidence is highly suggestive that the outbreak is associated with exposures in one seafood market in Wuhan," the WHO statement said, adding that the market was closed on Jan 1. "At this stage, there is no infection among healthcare workers, and no clear evidence of human to human transmission."

The Wuhan Municipal Health Commission said in a separate statement late on Sunday that 4 additional patients have been released and that no new cases have been discovered as of Saturday.

Another 717 people deemed to be in close contact with the patients remain under medical observation, the authority said.

The WHO said last week that a newly emerging member of the 'coronavirus' family of viruses that caused the deadly Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS) outbreaks was the likely cause of the outbreak.

Coronaviruses can cause infections ranging from the common cold to SARS. Some types cause less serious disease, while others can be far more severe.

Among 41 people confirmed as infected with the new viral pneumonia, one - a 61-year-old man with serious underlying medical conditions - died last week. Seven others are in critical condition, the Wuhan health authorities said.

The WHO said preliminary epidemiological investigations had found most cases were in people who either worked at or were frequent visitors to Wuhan's Huanan Seafood Wholesale Market.

"To date, investigations are still under way to assess the full extent of the outbreak," it added.