The government of Mexico City is launching a massive vaccination campaign throughout the city against swine flu, which has possibly killed 45 people and infected 943 nationwide.

The Mexican government confirmed on Friday the outbreak of the swine flu, and warned people to avoid crowds.

"It's a virus which mutated from pigs and transmitted to some human," Health Minister Jose Angel Cordova told Televisa television.

Health officials are now investigating the possible deaths and infections caused by the virus. Virus samples have been sent to laboratories in Canada for testing, they said.

The government also decided to close all schools in Mexico City and the center of the country to avoid spreading of the virus.

The World Health Organization, which has identified swine influenza as a potential source of a human flu pandemic, has also activated its global epidemic operations center.