The United States has enough of the antiviral medication oseltamivir, marketed by Roche Laboratories as Tamiflu, to treat about 2.3 million people.

But some 90 million people would need the medication in the event of a flu pandemic, said Hayden, adding the nation should have enough for 4.3 million people by year's end.

The H5N1 avian influenza virus has killed millions of birds across Asia and infected 116 people, killing more than 60 of them. Scientists are concerned the virus, currently known to pass to humans from birds, could mutate and be passed among humans.

A draft of the Bush administration's final plan for dealing with a likely pandemic flu outbreak shows the United States is unprepared for the potential disaster, The New York Times reported on Saturday.

Nearly 2 million people in the United States could die, and a large outbreak that began in Asia would likely reach the United States within "a few months or even weeks," the Times cited the report as saying.

More than 25 countries have stockpiles of anti-flu drugs, Hayden said, and 10 either have enough or have ordered enough to treat 20 percent to 40 percent of their populations.

At current capacity, it would take about 10 years and cost about 14 billion euros ($17 billion) to produce enough oseltamivir to treat 20 percent of the world's population, the flu specialist at the University of Virginia added.

Up to 30 percent of the population could come down with the flu, according to Hayden. "It would certainly cause a lot of hospitalizations and a lot of loss of life," he said.

The Infectious Diseases Society of America recommends that enough antiviral drugs be available to treat half of the population. Hayden said early treatment, preferably within two days of the onset of symptoms, was crucial to preventing complications and death.

US President George W. Bush on Friday asked vaccine makers to speed up flu vaccine production.