Toronto ? Global health officials warned travelers Wednesday to avoid Beijing and Toronto, where they might get the SARS virus and export it to new locations.

Canadian officials angrily said they would challenge the health advisory and declared their nation’s largest city still “a safe place.” Toronto is the first location outside of Asia targeted in efforts to contain the disease.

In Beijing, Chinese officials said all public schools would close today for two weeks, affecting 1.7 million children. Thousands of people trying to flee the outbreak packed the capital city’s train station and airport.

A major medical center in China’s capital, the People’s Hospital of Peking University, was closed today amid a SARS outbreak. More than 2,000 employees were under observation while the hospital was being disinfected.

Dr. David Heymann of the World Health Organization said the new travel alert, which includes China’s Shanxi province, was necessary because “these areas now have quite a high magnitude of disease, a great risk of transmission locally … and also they’ve been exporting cases to other countries.”

The advisory, which says any unnecessary travel to those locations should be postponed, will be reviewed again in three weeks, he said. Previously, WHO warned against non-urgent travel to Hong Kong and the Chinese province of Guangdong, where the virus was first reported last November.

Dr. Paul Gully, director general of Health Canada, said he would challenge WHO’s assertion in a letter. “Toronto continues to be a safe place,” he said.

Dr. Clifford McDonald, an official with the U.S. Centers for Disease Control and Prevention, noted that the CDC had not issued the same strong advice. The CDC has warned travelers to take precautions when visiting Toronto.

And Toronto medical officer Dr. Sheela Basrur said the outbreak, while serious, “is contained — largely in hospitals which is, frankly, where it belongs. So we don’t have widespread community spread.”

But Heymann, WHO’s communicable disease chief, said Toronto had not contained the disease. A major reason for WHO’s action, he said, is that a cluster of SARS cases among health workers in another country was traced to the Canadian city in the last week.

He would not say where the new cluster emerged, but there have been reports of at least three incidents of SARS being exported from Toronto. One involved a Toronto medical assistant who apparently spread SARS to her family in Manila before she died of it.

That case is the only reported one where an infected person from Canada is known to have triggered SARS in another jurisdiction.

There is no treatment for severe acute respiratory syndrome, which has symptoms similar to pneumonia. It has killed at least 250 people worldwide, out of more than 4,000 infected.

Canada has been the most affected area outside Asia, with 140 cases and at least 13 deaths as of Wednesday, all in the Toronto area.