The World Health Organization warned a global swine flu pandemic was imminent, as more nations confirmed cases of a deadly disease that has spread round the world in a matter of days.
Although most of those now affected are not thought to be in serious danger, the flu's spread from Mexico to every corner of the globe has deepened fears that modern air travel can spread disease faster than anything in history.
Nations from Asia to Europe to the Americas announced new confirmed and suspected cases of the flu, believed to be a new strain of virus that has combined existing varieties of bird, swine and common human influenza.
Margaret Chan, the head of the WHO, said the warning level was being raised to phase five on a 1-6 scale -- meaning the threat of a pandemic was imminent and that time was "short" for nations to put emergency plans into action.
"All countries should immediately now activate their pandemic preparedness plans," Chan said. "The biggest question right now is how severe the pandemic might be."
Officials in Mexico, the epicentre of the outbreak, said eight people were confirmed dead while 91 infected people were healthy. They said the suspected death toll from the disease was 84, about half the previous number.
Some experts have suggested that the virus has weakened as it was carried elsewhere. The only confirmed swine flu death outside Mexico was a Mexican toddler in the United States announced on Wednesday.
"Unfortunately I would anticipate that we will see additional deaths," said Richard Besser, the acting head of the US Centers for Disease Control (CDC).
US President Barack Obama ruled out closing the border between the two countries as part of measures to fight the spread of the illness.
"It would be akin to closing the barn door after the horses are out, because we already have cases here in the United States," Obama told a news conference. "This is a cause for deep concern but not panic."
Since the outbreak in the past few weeks, swine flu has quickly made its way around the world, and nations have stepped up checks at airports and distributed flu medicines to try to halt the spread of the disease.
In New Zealand, officials said the number of confirmed or probable cases was 13 -- all but one of whom were from a high school group that recently visited Mexico -- and that the number of suspected cases was at 104.
"The symptoms we are getting are still around the mild end of the spectrum of influenza symptoms," said Fran McGrath, New Zealand's deputy director of public health.
Switzerland became the fifth European country to confirm the virus, with one case in a man recently returned from Mexico. There are also cases in Austria, Britain, Germany and Spain. In South America, Peru reported its first case.
The WHO's phase five alert means widespread transmission from person to person, and with no vaccine against the swine flu strain, authorities are dependent on reducing human contact to fight the spread of the virus.
Mexico has shut down many public venues -- including popular tourist sites as well as all restaurants, bars and gyms in the capital -- while major cruise lines and tour operators have also halted trips to the country.
The government said the ultimate cost to Mexico from the flu crisis could be up to 0.5 percent of GDP -- as much as 70 billion dollars.
In addition to the airline and travel sectors, which were already suffering from the global economic downturn, pig farmers in many places have been hit hard by the swine flu crisis.
After Israel announced two more suspected cases, neighbouring Egypt ordered the immediate slaughter of all pigs in the country.
Many countries have banned imports of North American pork, leaving US pig farmers reeling even though the disease cannot be caught from eating the meat -- a fact that has led US authorities to stop calling it swine flu.
"We're calling it the 2009 H1N1 flu," the CDC's Besser said. "That's now the name for it."