On Saturday, the public health commissioner said about 75 students at a high school in the Queens are ill after their "likely" exposure to swine flu. The specimens were being sent to the US Centres for Disease Control for confirmation.
Gregory Hartl of WHO told CNN that the news of cases in New York and possibly Kansas"is amplifying, reinforcing the concern we have that the spread of this virus ... could potentially be a pandemic virus."
The declaration of an emergency in Geneva was given in a statement issued by WHO director general Dr Margaret Chan on WHO's website.
The events in Mexico and United States prompted her to convene a meeting of the "emergency committee," which reviewed the data and identified "a number of gaps in knowledge" about the epidemiology of the illnesses.
"The Committee nevertheless agreed that the current situation constitutes a public health emergency of international concern," her statement said.
Hartl explained that the declaration was a legal device that enables WHO to alert the rest of the world to start looking for evidence of the disease. (dpa)