New Zealand Prime Minister John Key said on Monday that New Zealand was well prepared to handle swine flu and has increased surveillance.

The health authorities has 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.

Health Minister Tony Ryall confirmed on Sunday evening that there were 10 positive influenza results from testing carried out on 13 students from Auckland's Rangitoto College who returned from Mexico on Saturday. They stayed in Mexico for a three-week Spanish language course.

Ministry of Health officials said there was no guarantee these students have swine influenza but consider it likely.

The results have been sent to the World Health Organization laboratory in Melbourne to ascertain whether it was the H1N1 swine influenza. The results would be known in a few days.

A teacher who traveled to Mexico with Rangitoto College has also been admitted to hospital with influenza symptoms, the Ministry of Health announced on Monday morning.

Ryall said a further three children, from Northcote College who also visited Mexico, have started developing symptoms.

The flu has killed up to 86 people in Mexico and likely sickened about 1,400 in the country since April 13.

The flu has spread far beyond Mexico's borders with 20 confirmed cases in five US states and suspected cases in Canada, France, Britain as well as New Zealand.

Key told TVNZ that the plan set up since the 2003 bird flu scare meant New Zealand had good stocks of the Tamiflu vaccine -- about 1.4 million treatments and the single gateway into New Zealand via Auckland meant control was easier.

Options included people not being allowed onto Air New Zealand flights if they were ill and those who arrive at Auckland being sent by a doctor stationed there since 5:00 AM on Monday for checks.

He urged people who suspect they may have the flu to see a doctor, for sick people to stay home and precautions like hand washing and covering mouths when sneezing to be taken.

The authorities will contact passengers from the same international flight as the Rangitoto College students who are believed to have caught the potentially deadly swine flu while in Mexico.

The students, teachers and their families were now in home quarantine for an unspecified period of time.

On Monday morning, hundreds of passengers arriving at Auckland airport from North America were greeted with a questionnaire and a public health warning about swine flu.

The Ministry of Health had stationed doctors and nurses at Auckland International Airport on Monday morning to screen passengers arriving on Air New Zealand flight NZ1 from Los Angeles, as another group of students arrived back from Mexico, the center of the outbreak of deadly swine flu.

Health officials said anyone who had traveled to North America in the last couple of weeks should consult their doctor if they began to feel unwell.

The New Zealand government is warning travelers returning from Mexico, Canada and the US state of Texas to see a doctor immediately if they develop any flu-like symptoms.

A notice posted on Sunday on the government travel website advises travelers to take the same precautions as for any seasonal influenza including receiving a flu vaccine, washing their hands often, covering coughs and sneezes, and staying home when ill.