MEXICO CITY: Governments around the world rushed on Sunday to check the spread of a new type of swine flu that has killed up to 81 people in Mexico and infected around a dozen in the United States. Mexicans huddled in their homes while U.S. hospitals tracked patients with flu symptoms and other countries imposed health checks at airports as the World Health Organisation warned the virus had the potential to become a pandemic. The epidemic has snowballed into a monster headache for Mexico, already grappling with a violent drug war and economic slowdown, and has quickly become one of the biggest global health scares in years. In New Zealand, 10 pupils from an Auckland school party that had returned from Mexico were being treated for influenza symptoms in what health authorities said was a likely case of swine flu, although they added none was seriously ill. The WHO declared the flu a "public health event of international concern." WHO Director-General Dr. Margaret Chan urged greater worldwide surveillance for any unusual outbreaks of influenza-like illness. While all the deaths so far have been in Mexico, the flu is spreading in the United States. Eleven cases were confirmed in California, Kansas and Texas, and eight schoolchildren in New York City caught a type A influenza virus that health officials say is likely to be the swine flu. The new flu strain, a mixture of various swine, bird and human viruses, poses the biggest risk of a large-scale pandemic since avian flu surfaced in 1997, killing several hundred people. New flu strains can spread quickly because no one has natural immunity to them. Reuters