China, Britain, Japan and other countries urged the World Health Organization on Monday to be cautious about declaring the arrival of a swine flu pandemic, fearing that a premature announcement could cause worldwide panic and confusion. WHO acknowledged their wishes.

As the agency opened its annual meeting, WHO Director General Dr. Margaret Chan said she had listened carefully to the concerns of member states and would follow their instructions.

'No one can say whether this is just the calm before the storm.'— Dr. Margaret Chan, World Health Organization

The new swine flu virus continues to spread rapidly, but the world is still short of facing a pandemic, Chan said, keeping the alert level at the current Phase 5 out of a possible six, indicating a global outbreak is likely.

China's Margaret Chan, center, Director General of the World Health Organization (WHO), speaks next to US Health and Human Services Secretary Kathleen Sebelius, left, and Mexican Health Minister Jose Angel Cordova Villalobos, right, on the first day of the 62nd World Health Assembly in Geneva, Switzerland on Monday. (Laurent Gillieron Keystone/Associated Press)"This virus may have given us a grace period, but we do not know how long this grace period will last," Chan said. "No one can say whether this is just the calm before the storm."

At Phase 6, the world has a swine flu pandemic — meaning there is an epidemic in at least two world regions.

Health experts from dozens of countries urged WHO to change its standards for declaring a pandemic, saying it should take into account whether the virus was causing severe or mild illness, not just how quickly it was spreading.

"We need to give you and your team more flexibility as to whether we move to Phase 6," said British Health Secretary Alan Johnson.

Chan repeated her warning that the virus could pose a grave threat to humans, even though only 76 out of 8,829 cases have proven fatal.

"A new influenza virus with great pandemic potential, the new influenza A (H1N1) strain, has emerged," she said.

Most deaths have occurred in Mexico, but there is global unease that the virus seems to be spreading easily from person to person and rapidly from country to country.

"We expect this pattern to continue," Chan said, adding it was unclear whether or when the world would move to the highest flu alert.

At least 40 countries now have confirmed cases — and the number of swine flu infections in Japan rose from four Friday to over 130 on Monday.

Chan said the virus has now spread to the Southern Hemisphere after breaking out in North America, and there was a risk it can combine with other flu strains circulating now among humans south of the equator.

Another concern is that swine flu might combine with the bird flu virus that has been circulating for several years, she said. Bird flu is much more deadly but less easily transmitted among humans than the swine flu virus.

Chan said WHO had not yet given manufacturers the signal to produce a specific swine flu vaccine for the new flu strain, but said it was essential that countries be careful with their medical resources.

"Manufacturing capacity for antiviral drugs and influenza vaccines is finite and insufficient for a world with 6.8 billion inhabitants," Chan said. "It is absolutely essential that countries do not squander these precious resources through poorly targeted measures."