The World Health Organization has raised its level of swine flu pandemic alert from phase 4 to 5, one step short of a full-scale pandemic, the WHO said on its website on Thursday.

"Based on assessments of all available information, and following several expert consultations, I have decided to raise the current level of influenza pandemic alert from phase 4 to phase 5," WHO Director General Margaret Chan said.

The WHO said nine countries have officially reported cases of swine influenza A/H1N1 infection.

"All countries should immediately activate their pandemic preparedness plans. Countries should remain on high alert for unusual outbreaks of influenza-like illness and severe pneumonia," she said.

"For the first time in history, we can track the evolution of a pandemic in real-time," Chan added.

In Mexico, which is thought to be the source of the outbreak, swine flu has been confirmed in 99 people, and eight people have died, according to Health Minister Jose Angel Cordova. Sanitary authorities, however, reported 17 suspected swine flu deaths in the past two days.

The outbreak of the deadly disease has resulted in the loss of over $55 million daily for Mexican retail, services and tourism sectors. Losses may top $500 million by May 6.

Swine flu concerns have prompted the government to shut education and entertainment facilities, as well as popular tourist venues in and around Mexico City. The country''s authorities declared May 1-5 days off.