MEXICO CITY --Mexico is canceling classes for millions of children in the heart of the country on Friday after influenza killed around 20 people in recent weeks.

Mexican Health Minister Jose Angel Cordoba said schools and universities in Mexico City and the surrounding area would be temporarily closed and advised people with flu symptoms to stay home from work.

We're dealing with a new flu virus that constitutes a respiratory epidemic that so far is controllable, Cordoba said on Thursday.

Canada's government advised doctors to be on the alert for reports of illness from people who recently traveled to Mexico, although it did not advise against visiting the popular beach vacation destination.

Mexico's flu season normally ends in February or March, but it has extended longer this year, the government said.

We recommend avoiding places or events with a lot of people unless strictly necessary, Cordoba said in an unusual late-night live statement to media.

About 79 people, possibly ill with the flu, are being treated in Mexico and that number has not increased in recent days, the Health Ministry said.

Worldwide, seasonal flu kills between 250,000 and 500,000 people in an average year.

In the United States, seven people have been diagnosed with a new kind of swine flu in California and Texas, the U.S. Centers for Disease Control and Prevention reported.

All seven people there have recovered but the virus itself is a never-before-seen mixture of viruses typical among pigs, birds and humans, the CDC said.

Canadian officials have been particularly sensitive to the international spread of respiratory illnesses since Toronto was hit by the SARS epidemic in 2003, which was blamed partly on a slow response to early disease reports.