The World Health Organization has raised the alert over the H1N1 swine flu virus to Phase 6 - a global pandemic. This does not indicate an increase in the severity of the disease, but rather a rise in global infection rates.

The H1N1 virus is the first global pandemic of the 21st century — and the first to be declared in 41 years. The flu has spread to 74 countries and infected 27,737 people, causing 141 deaths.

More than 100 people are now thought to have died of swine flu in Mexico, where the disease first broke out. The first fatality has been reported in the US, and there have also been confirmed cases of the disease in Spain, the UK, Germany, New Zealand, Israel and Austria.

WHO Director General Margaret Chan urged countries to activate their pandemic plans, saying: "It really is the whole of humanity that is under threat in a pandemic."

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