A bird flu pandemic could cost the global economy up to $800bn (£458bn), the World Bank has warned.
The global conference is taking place at the WHO in Geneva
The figure was made public at a World Health Organisation (WHO) conference in Geneva, where a global plan for dealing with a pandemic is being discussed.
It is "only a matter of time" until the deadly H5N1 virus becomes capable of human to human transmission and causes global chaos, the head of the WHO said.
The World Bank announced a $1bn emergency funding drive.
The three-day conference opened as China began a mass cull of six million poultry.
Presenting a report to the conference, the World Bank said that $800bn amounted to 2% of the global economy.
The World Bank proposed to fund $500m of grants and aid to countries hit by a pandemic, and hopes to raise a similar sum through donations.
"And it is fair to assume the shock during a flu epidemic could be even larger and last longer than Sars," said Milan Brahmbhatt, World Bank chief economist for the Asia-Pacific region.
Sars, or Severe Acute Respiratory Syndrome, caused widespread global panic before being contained in 2003, but pathologists view a potential bird flu outbreak as a vastly more dangerous proposition.
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.
At least 62 people have died of bird flu in Asia since the disease broke out in 2003.
Some 150 million birds have been culled worldwide as fears grow of a wider outbreak.
BIRD FLU OUTBREAKS IN 2005 (H5N1 STRAIN)
The H5N1 strain remained largely in South-East Asia until this summer, when Russia and Kazakhstan both reported outbreaks
Scientists fear it may be carried by migrating birds to Europe and Africa but say it is hard to prove a direct link with bird migration
EU has banned the import of captive live birds