At a global conference at the World Health Organisation (WHO) headquarters in Geneva, the World Bank has warned a bird flu pandemic could cost the global economy up to $800bn, which amounts to 2% of the global economy.
The Geneva conference is the first time representatives of the WHO, World Bank, the Food and Agricultural Organisation (FAO) and the World Organisation for Animal Health (OIE) have met to discuss the problem.
The World Bank also announced a $1bn emergency funding drive.
It is proposing to fund $500m of grants and aid to countries hit by a pandemic, and hopes to raise a similar sum through donations.
The figure was made public at the conference where a global plan for dealing with a pandemic is being discussed.
The three-day conference opened as China began a mass cull of six million poultry.
Lee Jong-wook, director-general of the World Health Organisation told the meeting of 600 health experts and planners that the world is experiencing the relentless spread of avian flu among migratory birds and domestic poultry.
The virulent H5N1 strain of avian flu, which first appeared in Hong Kong in 1997, is killing birds in 15 countries of Europe and Asia, he said, and it is inevitable that an avian flu virus - most likely H5N1 - will acquire the ability to be transmitted from human to human, sparking the outbreak of human pandemic influenza.
Lee said if the world is unprepared, the next pandemic will cause incalculable human misery - both directly from the loss of human life, and indirectly through its widespread impact on security, and no society will be exempt, no economy would be left unscathed.