International health and food safety agencies have appealed to donors for funds and technical assistance to help stop the spread of bird flu in Asia.
There are fears about the virus' spread
The agencies warned that the disease could become an influenza pandemic.
"We have a brief window of opportunity before us to eliminate that threat," said Jacques Diouf, head of the UN's Food and Agriculture Organization.
The appeal comes a day before Thailand hosts an international conference on ways of containing the disease.
The European Union and nearly a dozen governments, including China and the United States, are due to attend.
There are so far eight confirmed human deaths from bird flu: two in Thailand, and six in Vietnam.
The outbreak has also affected Japan, South Korea, Cambodia, Taiwan, Indonesia, Pakistan and Laos.
In other developments:
China confirms an outbreak of the virus among its duck population.
A six-year-old boy Thai boy dies from the disease.
- The World Health Organization (WHO) urges Indonesia to begin culling poultry affected by the virus.
- Hong Kong imposes a ban on poultry imports from China, Indonesia, Laos and Pakistan.
There are fears that the bird flu virus could mutate, attaching itself to a human flu virus which could spread between people.
"The spread of highly pathogenic avian influenza in several areas in Asia is a threat to human health and a disaster for agricultural production," the UN Food and Agriculture Organization (FAO), the World Organisation for Animal Health (OIE) and the WHO said in a joint statement.
"Although it has not happened yet, the so-called 'bird flu' presents a risk of evolving into an efficient and dangerous human pathogen," the three agencies warned.
AVIAN FLU ALERT
First jumped "species barrier" from bird to human in 1997
In humans, symptoms include fever, sore throat, and cough
Types which threaten humans are influenza A subtypes H5N1 and H9N2
"This is a serious global threat to human health," said WHO Director General Lee Jong-wook.
"This time, we face something we can possibly control before it reaches global proportions if we work co-operatively and share needed resources. We must begin this hard, costly work now."
FAO Director General Jacques Diouf said farmers in affected areas urgently needed to kill infected and exposed animals and "require support to compensate for such losses".
"The international community has a stake in the success of these efforts and poorer nations will need help," Dr Diouf said.
The agencies did not specify how much money was needed, but the technical assistance included diagnostic kits and protective gear for workers involved in the culling.
China's silence about bird flu was broken on Tuesday when the official Xinhua news agency reported the death of a flock of ducks in the south-west of the country, bordering Vietnam.
There had been mounting speculation about how China could have been spared from the outbreak which has been raging through the arc of countries surrounding it.
Thailand was criticised by the European Union on Monday for "non-transparency" in its dealings over the outbreak.
Prime Minister Thaksin Shinawatra, faced with accusations of a cover-up, has admitted his government initially kept quiet about its suspicions that avian flu had broken out, to avoid causing public panic.
Thai authorities have mounted a huge operation to cull all birds in the infected areas - more than 24 million have been destroyed so far.