The World Health Organization has declared the swine flu outbreaks in Mexico and the US a "public health emergency of international concern."

The WHO chief Margaret Chan has urged all countries to increase their surveillance.

The WHO made the decision after emergency talks with experts on Saturday.

Director-general Margaret Chan says there is a risk of the new disease spreading to other countries.

She urges health authorities worldwide to be on high alert for unusual flu cases.

Margaret Chan, WHO Director-General, said, "I think that at this point in time, it is very important that all regions of the World Health Organization work with our countries to heighten surveillance so that we know exactly whether this new disease is causing infection in human being in countries other than the US and Mexico."

Some of those who died are confirmed to have a unique version of H1N1 flu virus. The virus is a mix of human, pig and bird strains.

Gregory Hartl, WHO Spokesman, said, "We are at the beginning of the outbreak here, and there are a lot of things that we still don't know. We are not sure exactly of the transmission routes, where the initial infection came from, how efficient it is in transmitting.

The WHO stopped short of raising its pandemic level. The experts agreed more information is needed. The current alert level is Phase 3, which means no or very limited human-to-human transmission.

WHO officials are assessing the situation in Mexico. They are also helping with disease surveillance, laboratory diagnosis and managing cases.

(CCTV April 26, 2009)