BEIJING (AFP) — China may have experienced outbreaks of bird flu among poultry recently, the UN's Food and Agriculture Organisation said Wednesday, even though the government had yet to report any cases this year.

The FAO's comments come after eight people contracted the H5N1 bird flu virus in China this year -- five of whom died -- compared with just three cases in all of 2008.

"There must have been some virus circulation or possibly some outbreaks lately," Vincent Martin, senior technical adviser on bird flu for the FAO in China, told AFP.

But he said the FAO had received no reports of bird flu cases in poultry from the agriculture ministry since December, when an outbreak occurred in the eastern province of Jiangsu.

"There must be some suspicions of the disease reported to the Ministry of Agriculture, and some of those suspicions might have come up positive," he said.

"We are waiting to receive some reports describing the overall epidemiological situation and the results of investigations."

The number of cases in China this year has aroused some public concern, although the World Health Organisation has said the overall situation is "within expectations at this time of the year."

Cold weather encourages the spread of the virus, and the Lunar New Year holiday -- a risky period when hundreds of millions of people move across the nation to see relatives and eat meals that include poultry -- has just ended.

But Martin said the pattern this year was unusual.

"There are more cases than last year, including in places where the disease was not reported before like in Jiangsu province (poultry outbreak) or Shandong province (human case)," he said.

Lo Wing-lok, an infectious disease expert in Hong Kong, said that if no poultry outbreak in China was accompanying the current human cases, the latter could have been triggered by a mutation in the H5N1 virus.

"Maybe the virus has been changing, so that it becomes a more easily transmittable virus between bird and man," he said.

Experts fear the H5N1 virus could mutate into a form easily transmissible between humans, with the potential to kill millions in a pandemic, but there has been no evidence yet of this happening.

So far, 25 people have died from avian influenza in China since the disease re-emerged in 2003, according to World Health Organisation figures.