AFP - The swine flu crisis deepened Tuesday, with at least 16 countries far beyond worst-hit Mexico, including in Europe and Asia, reporting confirmed or suspected infections.
South Korea reported one probable case, while Australia and New Zealand reported more than 100 suspected infections, a day after the World Health Organization warned of a significant increase in the risk of a pandemic.
Mexico, the epicenter of the outbreak, said the likely toll from the virus stood at 152, with 20 deaths confirmed to be a result of the latest strain, as schools closed across the country.
The government has been criticized for failing to respond quickly enough to the first signs of the flu and of failing to quarantine close family members who could catch the disease or pass it on.
The number of confirmed cases in the United States jumped to 44, while Britain and Spain both said they had registered patients sick with swine flu, among almost 50 suspected and confirmed cases across Europe.
In Asia, South Korea said it was investigating one suspected infection, while New Zealand, which is already treating 10 people who are expected to prove positive, reported a further 56 suspected cases.
"It's a time for caution and concern, but not alarm," said New Zealand Health Minister Tony Ryall.
WHO officials in China said they were investigating several people with suspicious symptoms, but played down the chances that any were likely infected.
Australian authorities said they were investigating 45 possible cases and along with Japan urged nationals to consider returning home.
Tokyo went one step further, saying it would temporarily tighten visa restrictions for Mexican nationals as part of efforts to stop the virus entering the country.
It also booked 500 hotel rooms near Tokyo's Narita International Airport in case it needs them to quarantine infected travellers, Jiji Press reported.
In Europe, where the first case was confirmed in Spain on Monday, suspected cases were being monitored in Denmark, France, Ireland, Sweden and Switzerland.
Fears the virus disease could further hit the struggling global economy spooked investors, with stocks in Europe's leading markets sliding in opening trade, following sharp losses in Asia.
Oil prices continued to decline amid worries that the outbreak would hurt air travel and hit demand.
"The initial flu news has created the spectre of a potentially globally economic depressing event just as the markets were evaluating the prospects for economic recovery," said JP Morgan Research analyst Lawrence Eagles.
The World Health Organization's Keiji Fukuda said a pandemic was not inevitable and that while the hike in its alert level was a "significant step towards pandemic influenza, it's also a phase which says we are not there yet".
Fukuda warned "that in this age of global travel where people move around in airplanes so quickly, there is no region to which this virus could not spread."
UN chief Ban Ki-moon warned the new multi-strain virus, which is believed to be a mix of a human flu virus and an avian flu that first came from swine, risked triggering a global pandemic.
"We are concerned that this virus could cause a new influenza pandemic. It could be mild in its effect or potentially be severe," Ban told reporters.
"We don't know yet which way it will go but we are concerned that in Mexico most of those who died were young and healthy adults."
Influenza caused three epidemics during the 20th century, the worst being the Spanish flu between 1918 and 1919 that killed at least 40 million people, according to the WHO.
Although the US government has declared a public health emergency with 44 cases in five states, President Barack Obama urged calm.
The swine flu outbreak "requires a heightened state of alert, but it is not a cause for alarm," he told a gathering of the National Academy of Sciences.
Swiss pharmaceutical group Roche said it was ready to send out more stocks of the antiviral medication Tamiflu, some 220 million doses of which are in the hands of governments worldwide.
And British pharmaceutical giant GlaxoSmithKline also said it was "urgently" investigating how to boost production of its antiviral drug Relenza, as the race to develop a direct vaccine for the H1N1 strain gathered pace.