Churches stood empty in Mexico City yesterday and football matches were played to vacant stadiums, as soldiers and health workers patrolled the subway in an effort to prevent the spread of a deadly strain of swine flu.

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North of the border, in the US, doctors were advising people worried about the illness to buy painters’ masks from DIY stores as a precautionary measure. Authorities across the globe were torn between the imperative of slowing the spread of a potential flu pandemic and the need to avoid bringing every big city to a grinding halt.

Last night the US authorities were still allowing people to cross the border from Mexico, where it is thought that the swine flu emerged. But customs officials at the San Ysidro and Otay Mesa crossings were given protective clothing.

Michael Bloomberg, the Mayor of New York, said that the Centres for Disease Control and Prevention had confirmed that eight pupils at a city high school were infected with swine flu after some had returned from Cancún, in Mexico, two weeks ago.

In Mexico, health workers were screening bus stations and airports, handing out surgical masks and looking for possible flu cases. People were advised to seek medical attention if they suffered from multiple symptoms, which include fever, body aches, coughing, a sore throat, respiratory congestion and, in some cases, vomiting and diarrhoea.

Hundreds of public events were called off to prevent the spread of the virus in crowds. Zoos and schools have been closed, visits to juvenile correction centres suspended and restaurants were virtually empty.

Some who ventured out expressed a sense of bravado. Roland Guerrero, sitting at a city centre café, said: “They have blown this out of proportion. They say there have been 20 deaths here. But what is that in a city of 20 million? Nobody will be talking about this by Tuesday.”

But Ricardo Noriega, 63, a businessman who lives in Mexico City, said: “This is serious and the next few days will prove if they can contain it.”

In Spain, which has a large Mexican émigré population, seven suspected cases were being investigated. All had recently returned from Mexico. Spanish authorities were contacting passengers on the same flights as the people suspected of having the flu.

Canada confirmed six cases, but they were already recovering. Two suspected cases have been reported in France, nine in Colombia and one in Israel. In New Zealand authorities said that ten pupils were likely to have swine flu after a school trip to Mexico.

Traumatised by the “ghost town” memories of the severe acute respiratory syndrome (Sars) outbreak, Asian governments switched into crisis mode, racing to strengthen quarantining procedures. For Hong Kong, where Sars killed nearly 300 in 2003, the World Health Organisation’s weekend warning that this was a health event “of international concern” was especially chilling. The city was the focal point in 1968 of a flu pandemic that claimed a million lives around the world.

The World Health Organisation’s decision to raise the alert level was especially evocative because the agency’s head is Hong Kong’s former Health Minister, Margaret Chan, the doctor credited with pulling the city through the Sars outbreak.

The constant threat of bird flu mutating into a human pandemic has meant that many Asian countries now routinely use thermographic technology to screen passengers from areas where the fever may be present. Those checks are now being run on passengers arriving from Mexico, California and Texas. Countries that do not have the equipment are using medical questionnaires and other health checks.

With big travel agencies cancelling all flights to Mexico, and emergency health ministry hotlines overrun with calls, Japan’s Prime Minister, Taro Aso, convened the Cabinet crisis committee and ordered it to “stop the entry of swine flu at Japan’s borders”.

The White House said that President Obama’s health “was never in any danger”, despite reports that Felipe Solis, an archaeologist he met on a trip to Mexico last week, had died soon after from “flu-like symptoms”.

Robert Gibbs, the White House Press Secretary, said that based on the incubation period for swine flu, there was no reason for Mr Obama to be tested for the disease. Although the President is being briefed on the situation every few hours, Mr Gibbs insisted: “This is not a time for panic.”

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