WELLINGTON - Ten New Zealand teenage students who recently traveled to Mexico have tested positive for influenza and are "likely" to have contracted swine flu, Health Minister Tony Ryall said Sunday.

A new, multi-strain swine flu has flared in Mexico, and is feared to have killed more than 80 people, with the World Health Organisation (WHO) warning of "pandemic potential."

Ryall said in a statement that samples from the infected students had been sent to a WHO laboratory in the Australian city of Melbourne to determine whether they had contracted H1N1 swine influenza.

They already tested positive for influenza A, of which swine flu is a sub-set.

"Ministry of Health officials advise me there is no guarantee these students have swine influenza, but they consider it likely," the minister said.

"I am also informed none of the affected patients are considered seriously ill, and most in fact seem to be on the road to recovery."

The 10 were among a group of three teachers and 22 senior students from Rangitoto College in Auckland who returned home Saturday after a three-week trip to Mexico.

Thirteen students and one teacher had displayed flu-like symptoms and were quarantined in their homes while undergoing tests. One student spent Saturday night in hospital but had since been discharged.

Rangitoto College principal David Hodge said the students, aged 15-18, had spent most of their time in Mexico City on a Spanish language trip.

None had been "desperately" unwell and none had been at school and in contact with classmates, Hodge said.

"If it should eventuate that they have this flu, then it's been contained immediately, which is fantastic."

New Zealand's foreign ministry has issued a travel health notice for Mexico, California and Texas, where swine flu cases have been confirmed.

It advised anyone who had recently travelled to these areas and developed flu-like symptoms to seek immediate medical attention.

The Rangitoto school party returned to New Zealand from Mexico via Los Angeles.

The country's health ministry is implementing the early stages of its pandemic response plan, and is liaising with the WHO and Australian health officials.

A New Zealand-based animal diseases consultant, Roger Morris, said the country had stockpiles of the medication Tamiflu, which he said appeared to work against the current strain of influenza.