A school group from New Zealand's largest city of Auckland was being quarantined at home after returning from Mexico, New Zealand media reported on Sunday.
An emergency decree has been declared in Mexico following the outbreak of a new flu virus suspected of killing 81 people there. The World Health Organization has declared the outbreaks of influenza-like illness in Mexico and four U.S. states as a "public health emergency of international concern".
Twenty-two students and three teachers from Auckland's Rangitoto College were being quarantined at home in Auckland on Sunday after returning from Mexico, many with flu-like symptoms, Radio New Zealand reported.
The Auckland Regional Public Health Service said it hoped to know later on Sunday whether their illness is linked to the flu outbreak in Mexico and which has spread to four U.S. states.
The group arrived back in Auckland early on Saturday, when concerns were raised by a family doctor and a hospital specialist who treated them for flu-like symptoms.
Auckland health authorities said 13 students and one teacher from a group of 22 students and three teachers are unwell, and one of the students was in hospital on the North Shore.
It added that the others were in home isolation in Auckland.
Mexican President Felipe Calderon issued a decree on Saturday giving the government special powers to run tests on sick people, to isolate those who are ill, enter homes or workplaces and regulate air, sea and land transportation.
Of the 81 deaths suspected of being caused by swine influenza in Mexico, 20 are confirmed. More than 1,300 people in Mexico were suspected to be infected with the flu.
New Zealand's Ministry of Foreign Affairs and Trade has issued a Travel Health Notice for Swine Flu in Mexico, California and Texas.
In New Zealand, normal border control procedures remain in place while authorities keep watch on the progression of the disease.
The Ministry of Health was implementing the early stages of its pandemic response plan but said at this stage there is no indication it will be needed. The ministry was continuing to liaise with the World Health Organization and Australian officials.
Auckland Airport said it was keeping a watching brief on the situation, though Air New Zealand does not fly directly into New York or Mexico.