The World Health Organization has declared the first influenza pandemic in more than 40 years, as infections of the H1N1 swine flu virus continue to spread.

WHO Director-General Margaret Chan speaks during a press conference at WHO headquarters in Geneva, Switzerland, 11 Jun 2009

WHO Director-General Margaret Chan announced Thursday that the U.N. agency is raising the pandemic alert level from Phase 5 to the maximum Phase 6 following a meeting of experts in Geneva.

Officials note that declaring a pandemic does not mean the disease has become more severe, but that there is an increasing number of infections in different geographical locations.

Chan said the virus is likely to remain moderate at least in the early days of the pandemic, though she warned that the virus could change.  She said officials do not expect a jump in the number of severe or fatal infections, which have been relatively small worldwide.

Chan said nearly 30,000 cases have been reported in 74 countries. 

Chan also said WHO will continue to recommend no restrictions on travel, and no border closures.  She urged countries to be vigilant.

WHO says a Phase 6 alert will likely get governments to spend more money to contain the outbreak, and trigger drug companies to speed up production of a vaccine.

In Hong Kong, authorities are closing all kindergartens and primary schools for two weeks after 12 students tested positive for the virus.  Hong Kong's chief executive Donald Tsang said the cluster of local human swine flu cases does not have a known source of infection.

Also Thursday, authorities in the western German city of Duesseldorf confirmed at least 26 cases of swine flu among students at a Japanese school in the city.

Australian officials announced Thursday that four swine flu victims were admitted to intensive care wards after a spike in H1N1 cases in the country.  Australia has more than 1,200 reported cases.

The United States has recorded the most cases, with more than 13,000, although Mexico has the most deaths, which currently stand at more than 100. 

The WHO says 144 people have died from the virus.

The last time the WHO declared a pandemic was in 1968 following the outbreak of the Hong Kong flu which killed at least one million people.

Some information for this report was provided by AFP and AP.