Bird flu epidemic may kill millions worldwide

"If there was a flu pandemic tomorrow we would not be ready. The clock is ticking and when the pandemic strikes it will be too late," said WHO spokeswoman Christine McNab.

Despite warnings at the United Nations by US President George W. Bush and French Prime Minister Dominique de Villepin calling for international cooperation to confront the "first pandemic of the 21st century", the international community was far from prepared.

"There is very good momentum, but a lot of work remains to be done," McNab said.

Of the 192 members of the UN just 40 countries had drawn up detailed plans for combating an outbreak in humans of a mutation of the H5N1 virus which could, like the 1918 Spanish influenza pandemic, kill millions of people.

For the WHO it is question of when, not if, the virus crosses over to a strain affecting humans, experts said.

"The question is, 'When is it going to happen?' I don't think anybody has the answer to it... We have to be on the lookout for any time, any day," the WHO specialist on the virus, Margaret Chan, said in July.