A Mexican soldier carries a pack of masks which will be distributed to pedestrians in Mexico City, capital of Mexico, April 25, 2009. Mexican government has handed out 6 million masks for free to citizens of Mexico City since April 23. The World Health Organization (WHO) on Saturday declared the swine flu outbreak in Mexico and the United States a "public health emergency of international concern" and urged countries to be alert.

A Mexican soldier hands out masks in Mexico City, capital of Mexico, April 25, 2009.

A Mexican soldier hands out masks in Mexico City, capital of Mexico, April 25, 2009.

A Mexican soldier hands out masks in Mexico City, capital of Mexico, April 25, 2009.

A Chinese tourist puts on a mask in Mexico City, capital of Mexico, April 25, 2009.

A Mexican busker wearing a mask plays the violin in Mexico City, capital of Mexico, April 25, 2009.