The chicken, a gift to a family that lives in a village in a no-man's land strip on the Hong Kong-Chinese border, was said by officials to have been bought in southern Guangdong province.

However, the head of Hong Kong's Centre for Health protection Thomas Tsang said Chinese officials had last week sworn that the province was virus-free.

"We visited before Chinese New Year and ... (an official) informed us there were no cases of H5N1," Tsang told reporters.

World health and food experts tracking the disease, which has killed some 85 people since exploding across Asia in 2003, believe the emergence of bird flu in Hong Kong suggests there are holes in China's reporting procedure.

"I'm not so sure it's a problem of the central government; it's more one of the local governments," said Guo Faosheng, technical adviser to the United Nations Food and Agriculture Organisation (FAO) mission in China.

"The central government is being open, we think, but the local governments have different interests to protect. That's where the problem with reporting is happening," Guo added.

He said local officials were reluctant to report all bird flu cases, as they feared a drop in either business investments or tourist numbers in their respective regions should a serious outbreak be detected.

"Alternatively, they may simply not realise they have bird flu -- in areas that have been vaccinated, the disease would still be present even if birds were not falling sick," he added.

The incident has rekindled memories of China's cover-up in 2003 of the extent of an outbreak of the then unknown pneumonia-like Severe Acute Respiratory Syndrome (SARS).

Medical experts say the reluctance of Chinese authorities to admit to the presence of SARS hindered efforts to identify and ultimately stop a worldwide outbreak that claimed almost 800 lives, 10 percent of the 8,000 infected.

China was also accused of playing down and being too slow to react to bird flu when it first emerged on the mainland.

Subsequent censure by the European Union and the the World Health Organisation (WHO) has pulled the country's health chiefs into line.

However, experts have privately expressed concern that authorities sometimes lapse into their old ways. For instance, they criticised a media blackout when H5N1 was discovered among birds at Qinghai Lake in northern China last May.

International health experts concede that the vastness of China and its largely primitive infrastructure make it difficult for authorities to monitor every part of the country for bird flu outbreaks.

However, they also feel obliged to temper their criticism out of fear of being expelled by an over-sensitive regime that rarely brooks censure.

Nonetheless, WHO officials say that by comparison to China's earlier behaviour, matters are now far more satisfactory.

"I think they learned their lesson after SARS," the WHO's China spokeswoman Aphaluk Bhatiasevi told AFP earlier.

"The government has realised that this issue is a big problem," Bhatiasevi added.

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