Asia's pandemic response system is now being tested, after the swine flu strain that originated in Mexico spread to at least two countries in Asia.

South Korea confirmed Saturday that a nun who recently returned from Mexico has come down with the virus.

Authorities in Hong Kong are working with regional counterparts to track down dozens of people who could have been exposed to a Mexican tourist who has been diagnosed with swine flu.

China suspended direct flights from Mexico. The Mexican tourist in Hong Kong first landed in Shanghai on an AeroMexico flight before taking a China Eastern flight to Hong Kong. Health officials in Beijing said they have quarantined more than a dozen people who were on the same flights. Taiwan is seeking  other passengers who were on the AeroMexico flight to Shanghai who made connections to the island.

In Hong Kong, Dr. Gabriel Matthew Leung, undersecretary of health, said people who had traveled to Mexico will be closely scrutinized at the airport and land borders. 

"Be the passengers be Mexican or other nationalities they will be taken through a special route at immigration point whether they have come in by plane or land. These passengers be a visiting health station for further tests," he said.  "If passengers are showing symptoms of this flu while in the airplane and they have been from Mexico then all airline staff, if they feel that passengers look as if they might have contracted the flu, then they have to make an official report and relevant officials will approach the plane for testing of those passengers."

Mexico is the epicenter of the outbreak of swine flu.  The World Health Organization says there are more than 600 cases of the flu globally. Confirmed flu victims have been reported in many countries including the U.S., Canada, New Zealand, Israel, Switzerland and Denmark. The WHO has already raised its global pandemic alert to its second highest level, signaling an "imminent pandemic".

Hong Kong, which was hardest hit by the Severe Acute Respiratory Syndrome outbreak in 2003, has taken the most aggressive actions yet in Asia to contain the spread of the virus. Health authorities here said they will not hesitate to take even tougher measures to stop the spread. More than 200 guests at the hotel where Mexican victim stayed are being quarantined for 7 days.