GENEVA (AFP) - Millions of people could die around the world if bird flu spreads out of control, and most countries are totally unprepared for such an event, the UN's World Health Organisation says.

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.

Of the 192 members of the UN just 40 countries had drawn up detailed plans for combatting 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.