MEXICO CITY - Mexicans took new precautions Sunday amid fears that a new flu epidemic believed to have killed up to 81 people in the country could reach "pandemic" proportions and spread to the United States and worldwide.

Mexican Health Minister Jose Angel Cordova raised the probable death toll from the new multi-strain swine flu in Mexico to 81, including 20 already confirmed.

Earlier, Mexican President Felipe Calderon published an order giving his government extraordinary powers to tackle the deadly outbreak, as at least two new cases were reported in the United States, bringing the total infected there to 10.

"This virus has clearly a pandemic potential," World Health Organization director general, Margaret Chan, said on Saturday.

The Geneva-based UN agency branded the outbreak "a public health emergency of international concern," following a meeting of its emergency committee.

In a statement it said it was recommending that all nations "intensify surveillance for unusual outbreaks of influenza-like illness and severe pneumonia".

In Mexico, 13 new suspect cases were reported in the past 24 hours and a total of 1,324 patients with flu symptoms were under investigation, Cordova said.

The Mexico government has upped emergency measures that were put into place only on Friday.

Officials have canceled hundreds of public events and closed schools for millions of students in and around the capital.

Schools in those areas and also San Luis Potosi in central Mexico, the third most affected area, will remain closed until May 6, Cordova said.

The traditional Sunday mass was suspended in Catholic churches throughout the country.

Many Mexico City residents wore freely-distributed surgical masks on the streets Saturday, after authorities urged people to avoid contact in public.

Apart from the capital, four other deaths were reported in central, northwest and southern Mexico.

Mexico City Mayor Marcelo Ebrard said that more than 500 sporting and cultural events had been canceled for at least 10 days.

Mexico City authorities have said they had more than one million doses of suitable antiviral drugs, in an urban area of some 20 million.

The government also assured citizens it had "sufficient" funds reaching 450 million dollars to combat the epidemic.

Across the northern border, health authorities in the central US state of Kansas confirmed two cases of swine flu on Saturday, bringing the total number of cases in the United States to at least 10.

One victim was still ill, while the other had recovered, Kansas health authorities said. One patient had recently traveled to Mexico.

On Saturday, New York officials said eight to nine students at a New York City school were suspected of having swine flu, although test results were still pending.

Eight others in the United States - six in California and two in Texas - were confirmed to have come down with a similar strain of the flu found in Mexico, according to the CDC.

All eight have recovered, the CDC said, with only one needing hospitalization.

In London, a hospital announced that British Airways steward admitted with "flu-like symptoms" after arriving on a flight from Mexico City had tested negative for swine flu.

But in Wellington, New Zealand Health Minister Tony Ryall said 10 teenagers who had recently traveled to Mexico have tested positive for influenza and are "likely" to have contracted swine flu.

With these cases in mind, Anne Schuchat of the US Centers for Disease Control and Prevention (CDC) said her agency did not think at this time "that containment is feasible."

The CDC said some Mexican victims had died from the same new strain of swine flu that affected eight people in Texas and California.

Dave Daigle, of the CDC, said a bird flu strain, two swine flu strains and a human strain had combined for the first time.

"The most worrying fact is that it appears to transmit from human to human," said WHO spokesman Thomas Abraham.

These features, along with the fact that unusually young healthy adults have fallen victim in Mexico, and not the very old or very young, have given rise to fears of an epidemic or even a pandemic.

According to the WHO, pigs have already been factors in the appearance of two previously unknown diseases that gave rise to pandemics in the last century.

If a pig is simultaneously infected with a human and an avian influenza virus, it can serve as a "mixing vessel" for the two viruses that could combine to create a new, more virulent strain.