New Zealand's health authorities last night put the alert status for response to a potential influenza epidemic up from white to yellow, a stand-by phase which is one below the code red response phase.
Ten Rangitoto College students have tested positive for influenza A after they came down with mild flu symptoms on returning to New Zealand on Saturday.
Their tests will be sent to the World Health Organisation (WHO) laboratory in Melbourne for further testing to confirm whether it is actually swine flu.
It could take days for the results to be returned but Health Minister Tony Ryall said it was "highly likely" to be swine flu.
Mexican officials have put the death toll from the new flu strain at 81 and 1300 sick, while 10 people were believed infected in the United States and there were two possible cases in France.
WHO warned on Saturday that the virus had the potential to become a pandemic, labelling the current outbreak "a public health emergency of international concern".
Three other New Zealand school groups have been in Mexico. A group from Northcote College had already arrived in Auckland and two more, from Pinehurst and Westlake Girls' High Schools, were yet to return home. Their conditions were unknown.
The Rangitoto College group, three teachers and 22 students, returned to Auckland on Air New Zealand flight NZ1 from Los Angeles yesterday.
The flight carried 364 passengers plus crew and they were being contacted and told to see their doctor if they developed flu symptoms.
All students from the Rangitoto group were being kept in voluntary quarantine at home. Their families were also included in the quarantine.
Deputy director of public health Darren Hunt said anyone who had travelled to North America in the last couple of weeks should consult their doctor if they began to feel unwell.
"If people are sick we really need to know about it, the doctors and nurses really need to know about it, rather than people trying to manage symptoms -- particularly people who have travelled to North America."
Middlemore Hospital has released Tamiflu, originally stockpiled in response to a potential bird flu outbreak in 2003, to treat the patients and those who have contact with them.
The effectiveness of Tamiflu on swine flu was not yet confirmed, but reports from Mexico said it was effective, Mr Hunt said.
Rangitoto College principal David Hodge said the students, aged from 15-18 in years 11-13, had spent most of their time in Mexico City on the Spanish language trip.
The affected students had not been at school and the school will open today without them.
The influenza scare comes after China and Hong Kong bore the brunt of the Severe Acute Respiratory Syndrome (SARS) in 2003 that killed nearly 800 people, most of them in Asia, bringing air travel here to a near-standstill and battering the region's economies.
The same year, the H5N1 strain of bird flu re-appeared in Asia.
It has since killed 257 people, according WHO, and officials have long warned that the virus could become a global pandemic if it mutates into a form that is easily transmissible between humans.
