(Video APTN)

The World Health Organisation on Thursday was likely to declare the first flu pandemic in 41 years as swine flu infections continued to climb in the United States, Europe, Australia, South America and elsewhere.

Officials at UN missions in Geneva also said they expected the announcement of a pandemic.

A declaration of a pandemic would push drug makers to fast-track production of a swine flu vaccine.

Australia on Thursday announced that the number of confirmed cases stood at 1,275.

Four patients with swine flu are fighting for their lives in intensive care units of Melbourne hospitals.

But Health Minister Nicole Roxon said on Thursday that did not mean that the virus has become more dangerous.

Roxon said the virus has proved relatively mild with only 25 of those infected needing hospital treatment.

She said most of the critically ill had other complicating medical conditions.

"It can be easily treated and really our major focus is on ensuring we can reduce the spread where possible," Roxon said.

In Hong Kong, the government ordered all kindergartens and primary schools closed for 14 days after a dozen students tested positive for swine flu in the territory's first local cluster of cases.

Chief Executive Donald Tsang said 12 students at a local secondary school had tested positive for the virus and that authorities had not been able to immediately determine how they contracted the sickness, indicating it likely had spread locally within the community.

At least one of the infected students, a 16-year-old girl who tested positive late on Wednesday, had not travelled overseas recently, according to a government statement.

Tsang said schools would be closed starting on Friday to deter the spread of the virus, as authorities shifted their preparedness level from "containment" to "mitigation".

The closure will affect nearly 510,640 students at 1,626 schools, according to enrolment figures from the 2008-2009 academic year.

The new infections brought the total number of cases in the city to 60 after the first domestic transmission of swine flu in a 55-year old man was confirmed on Wednesday.

In the Philippines, the health chief said swine flu cases in the country had risen to 92, the highest number in Southeast Asia.

Health Secretary Francisco Duque said all 15 new cases confirmed on Thursday were Filipinos, including an elementary school student in northern Nueva Ecija province.

Classes in that school have been suspended.

On Tuesday 13 students were confirmed to have been infected at Manila's De La Salle University, including two Japanese.

On Thursday, all incoming visitors were screened for fever by student nurses.

Thailand's Public Health Ministry has confirmed 30 new cases of swine flu, bringing the country's total to 46 on Thursday.

Thai Prime Minister Abhisit Vejjajiva told reporters at the government house that 17 cases were detected in the seaside resort of Pattaya.

"They are staffers of an entertainment venue. Public Health Minister is now inspecting people who might have been in contact with them. As for those infected, they are now taken care of and no one showed signs of serious conditions," he said.

The other 13 cases include four students in Bangkok who attended a school where an earlier case had been detected.

This prompted Saint Gabriel School where students found infected to be closed for a week starting Friday.

Health ministries in Thailand and Indonesia said Thursday they had received an e-mail alert from the WHO advising them that a pandemic would be declared as early as midnight local time.

The world is in phase 5 of WHO's pandemic alert scale, meaning a global outbreak is imminent. Moving to phase 6, the highest level, means a pandemic has begun.

The last pandemic - the Hong Kong flu of 1968 - killed about 1 million people. Ordinary flu kills about 250,000 to 500,000 people each year.