'I hope they will be taking samples for storage, if not for analysis,' he said. 'It could indeed destroy the evidence.'

The Guangdong government has ordered the culling of 10,000 civet cats in the province before Saturday to cut off a possible source of infection.

Mr Gilbert described the decision as radical as there were no published journals or confirmation that civet cats were spreaders of the Sars virus.

The WHO also urged that great caution be exercised in carrying out the cull in order to prevent those taking part from contracting the virus.

'We have to make sure that the situation won't be [made] more risky by more procedures,' said Julie Hall, the WHO's Sars team leader in Beijing. 'We hope they will ensure that people doing the slaughter are protected. There is a potential hazard there.'

Asked if it was a mistake for Guangdong to lift the ban on the civet cat trade last year - a move described at the time by WHO experts as premature, Henk Bekedam, the WHO's chief representative in Beijing, said he understood the pressure and he was impressed by the regulations put in place by the authorities.

The experts from the global health body also called for the mainland to continue to carry out research to confirm if civet cats were the carrier of the Sars virus, and share the results with international scientific journals.

Asked about the findings by Guangdong scientists that the virus found in civet cats bears similar DNA sequencing with the virus found in the Sars patient in Guangdong, Ms Hall said she hoped the data could be shared with international medical journals.

The experts also warned that civet cats may not be the only possible carrier of the virus and called for more in-depth research to be carried out.

Mr Gilbert said it was still not known if civet cats spread the virus only when they were domesticated and under stress.

He said the WHO was told about the planned cull yesterday.