MEXICO CITY - Governments around the world acted to stem a possible flu pandemic on Monday, as a virus that has killed 103 people in Mexico and spread to North America was confirmed to have reached Europe.

While the swine flu virus has so far killed no one outside Mexico, the fact that it has proved able to spread quickly between humans has raised fears that the world may finally be facing the flu pandemic that scientists say is long overdue.

Shares and oil prices fell in Asia and Europe, as investors feared a further shock to an already fragile global economy, if trade flows are curbed and manufacturing is hit.

The MSCI world equity index fell 0.7 percent, and U.S. index futures suggested a fall of more than 1 percent on Wall Street.

Spain became the first country in Europe to confirm a case of swine flu when a man who returned from a trip to Mexico last week was found to have the virus.

But his condition, like that of 20 cases identified in the United States and six in Canada, was not serious. A New Zealand teacher and around a dozen students who recently returned from Mexico were also being treated as likely mild swine flu cases.

Cases of the flu, which has components of classic avian, human and swine flu viruses but has not actually been seen in pigs, were also suspected in Britain, France, Italy and Israel.

Many countries have stepped up surveillance at airports and ports, using thermal cameras and sensors to identify people with fever, and the World Health Organization has opened its 24-hour war room command center.

The European Union's health chief urged citizens to avoid non-essential travel to areas affected by swine flu, and the European Commission called an urgent meeting of health ministers.

U.S. EMERGENCY

The United States declared a public health emergency on Sunday. Although most cases outside Mexico were relatively mild, a top official at the Centers for Disease Control and Prevention said she feared there might be U.S. fatalities.

The WHO has declared the flu a public health emergency of international concern that could become a pandemic, or global outbreak of a serious disease.

Its emergency committee was due to decide on Monday whether to raise its pandemic alert level, currently at 3 on a scale of 1 to 6.

If we go to phase 4 because of the swine flu virus, it basically means that we believe that a potential pandemic virus has potentially shown it can transmit from person to person and cause large outbreaks, WHO Acting Assistant Director-General Keiji Fukuda said on Sunday.

But so far there have been no broad recommendations to limit international travel.

In the financial markets, travel and leisure stocks such as Hong Kong's Cathay Pacific Airways and British Airways nevertheless fell sharply, whereas makers of drugs and vaccines, such as Roche, were higher.

The threat of the pandemic will add further weakness to global trade, said Justin Urquhart Stewart, investment director at Seven Investment Management in London.

We saw with SARS tangible percentage points knocked off the index, and that was in a buoyant time. Put that in a weaker time and it is likely to be more unpleasant.

An outbreak of the SARS respiratory virus in 2003 was largely limited to Southeast Asia and cost the region's economy around 0.6 percent of GDP.

The World Bank estimated last year that a global flu pandemic could cost $3 trillion and cut world GDP by 5 percent.

Oil prices fell more than 4 percent to below $50 a barrel on Monday, pressured partly by expectations the world economy could suffer if a pandemic materializes.

Mexico's peso fell more than 3 percent on Monday.

MEXICO SLOWS TO A HALT

Japan's cabinet held a special meeting and said it would prioritize production of a new vaccine, although this process usually takes months.

In Mexico, the center of the swine flu outbreak, life has slowed dramatically in cities as schools have been closed and public events called off to slow the spread of the virus.

Many in Mexico City spent the weekend hunkered at home or wore blue surgical face masks handed out by truckloads of soldiers to venture out onto strangely hushed streets. The city government considered halting public transport.

Health Minister Jose Angel Cordova said on Sunday that the flu had killed 103 people in Mexico, and about 400 people had been admitted hospital. But he noted that a majority of infected patients had recovered.

Health authorities across Asia tried to give reassurance, saying they had enough stockpiles of anti-flu drugs to handle an outbreak.

Guan Yi, a virology professor at the University of Hong Kong who helped to fight SARS and bird flu, said a pandemic looked inevitable.

I think the spread of this virus in humans cannot possibly be contained within a short time ... there are already cases in almost every region. The picture is changing every moment ...

We are counting down to a pandemic.