The World Health Organization (WHO) today called for measures to prevent a flu pandemic in humans.
The call came after China said a deadly strain of bird flu was found in pigs, adding to signs that an outbreak among people was likely.
The UN health body said the Chinese discovery had raised its level of concern about the possibility that the virus, which originates in birds, could move into other animals and mutate into a strain deadly to humans.
A strain of bird flu blamed for 27 deaths in Asia this year was found in Malaysia this week and hundreds of birds have been gassed and their carcasses burned to contain the outbreak. China said on Friday it had found pigs infected with bird flu.
"We would urge two things, that there be heightened surveillance in pigs and then to take appropriate measures," said WHO spokesman in Geneva Mr Dick Thompson. "Then we would urge countries to step up their pandemic prevention measures."
The latest deaths from the H5N1 strain of avian influenza were of three people in Vietnam earlier this month.
"In the past, we have seen avian influenza move into pigs and then move into humans. That may be what is happening again," Mr Thompson said. "It could produce a pandemic strain."
Mr Thompson said influenza pandemics came in cycles, historically. "We know there will be a pandemic, we just don't know when it will be," he said.