By Guy Newey

HONG KONG - Hong Kong authorities Thursday ordered all primary schools in the city to be closed for two weeks after the first cluster of local swine flu cases was found.

The move came after 12 pupils at a city secondary school were found to have contracted the A(H1N1) virus, chief executive Donald Tsang told reporters.

Tsang said authorities were unable to identify the source of the infection, making it the first "cluster" of human swine flu cases in the city without a known link to those travelling overseas.

All primary schools, kindergartens, child care centres and special schools would be shut for 14 days from Friday in an effort to control the spread of the virus, Tsang said.

"Given the global situation, (for) Hong Kong to have its own local cases is simply inevitable," Tsang said.

"I believe the fellow citizens and the government have done all we can in postponing the arrival of the first indigenous case."

The move to shut primary schools rather than secondary schools was made because young pupils are more vulnerable to catching the virus, he added.

He added that individual secondary schools would be closed if there was a confirmed outbreak.

The latest move came more than a month after Hong Kong officials confirmed Asia's first swine flu case, sparking the week-long quarantine of around 300 guests and staff at a city hotel where the carrier had briefly stayed.

The move received some criticism as being over-zealous, and none of those who were trapped in the hotel contracted A(H1N1).

Authorities defended the quarantine as prudent and said such measures would help delay the spread of the virus.

Hong Kong is very nervous about infectious diseases following the outbreak of the SARS virus in 2003, which killed 300 people here and a further 500 around the world after one carrier spread the disease in a city hotel.

There have been around 50 confirmed cases of human swine flu infection in Hong Kong, but all the previous cases caught the virus while travelling abroad.

Housewife Cathy Wu said the decision could affect her 11-year-old daughter's preparation for exams, as she tries to win a place at a good secondary school.

"She has already started the exams which are really important for her, but now we just don't know whether we should carry on revising," she told AFP.

"It's good to be careful, but I think they (the government) should consider each case and have the suspension after the exams."

The city has set up tough measures at entry ports, including temperature screening and asking every visitor to fill in a health declaration form.

Since the A(H1N1) virus was first discovered in the United States and Mexico in April, 74 countries have reported more than 27,000 cases including 141 deaths, the World Health Organization (WHO) has said.

The WHO was on Thursday to consult with its emergency committee of flu experts, who could recommend the declaration of a global swine flu pandemic, a spokesman said.

So far the WHO has left its six-level pandemic alert scale unchanged at phase five - signalling that a pandemic is "imminent."

But if it determines that there are sustained local transmissions outside the Americas, it could raise the alert to six - suggesting a full-blown pandemic.