BEIJING — Alarmed by the spread of bird flu beyond East Asia, nations pledged nearly $2 billion Wednesday to fight the disease, far exceeding expectations at the fundraising conference in Beijing.

The United States alone promised $334 million.

The World Bank had appealed for at least $1.5 billion to stave off a potential bird flu pandemic that could kill millions worldwide.

David Nabarro, the U.N. coordinator on avian and human influenza, described the $1.9 billion in pledges as "quite extraordinary."

"What we've seen today is that the world really does care and wants to respond effectively to the threat of avian influenza and a possible human pandemic," he told reporters.

The World Bank has said about 45 percent of the funding would be spent in Vietnam, Cambodia, Indonesia, Thailand and Laos — countries where the H5N1 virus is already endemic.

Although primarily a disease affecting poultry, the virus has jumped to humans, killing 77 people in East Asia since 2003.

With a mortality rate of over 50 percent, experts are worried that the virus could mutate into a form that spreads easily from person to person.

The gathering in Beijing took on a new sense of urgency after Turkey reported four deaths from the virus this month, the first outside East Asia.

"There's no time to waste," U.N. Secretary-General Kofi Annan said in a taped address to the conference. "Let's ensure that we are ready."

The United States would take a leadership role in helping to manage the funds and ensure that they are channeled to where they can be of most use, said the U.S. coordinator for health, science and the environment, Nancy Powell.

The United States pledged $334 million, the second highest amount after the World Bank's $500 million. The United States also said it will invest billions of dollars over the next three years to develop a human vaccine.

Japan donated $159 million, while China — which has reported eight human infections, five of which have been fatal — said it would donate $10 million.

Chinese Prime Minister Wen Jiabao also promised that China would work with the international community and be open and forthcoming with information and samples of the virus.

"Money is not the only answer, but without it nothing can be done," said Dr. Lee Jong-wook, director-general of the World Health Organization.

On Tuesday, EU Health Commissioner Markos Kyprianou said the EU had increased its commitment to $121 million, about $20 million more than it announced last week.

The 25 member states were also expected to pledge about $120 million in total, he said.

"Never before has humankind had a window of opportunity to prepare for the event of a pandemic before it actually happens," he said. "And now we know what needs to be done."

The WHO said Swiss drug maker Roche Holding AG has agreed to donate another 2 million courses of the antiviral drug Tamiflu to help poor countries battling the disease. Tamiflu is believed to be most effective in treating bird flu in humans.

Roche last year donated 3 million courses of the drug to WHO for a global stockpile that would be distributed wherever a pandemic flu strain emerged, she said.

Company officials have said about 150 million treatments are expected to be produced this year.

The funding conference, co-sponsored by the World Bank, European Commission and the Chinese government, follows a global bird flu coordination meeting held two months ago in Geneva, which brought together participants from 100 countries.

Based on the damage that severe acute respiratory syndrome, or SARS, caused to Asia's economy after it emerged in southern China in 2002, the World Bank says a flu pandemic in humans could result in $800 billion in global losses in a year.