New Zealand now has six confirmed cases of swine flu, but the total number of suspected cases and of those in isolation or quarantine is on the way down.

New Zealand had six confirmed cases of influenza A (H1N1), up two since yesterday, deputy director of public health Dr Fran McGrath said this evening.

The two new cases had been on the probable cases list prior to today. With no new probable cases, this number was now down to 11 after the removal of the new cases.

One of the new confirmed cases was a student from Hawke's Bay who returned to New Zealand on April 28 from North America on a Lindisfarne College school trip.

That student remains in isolation at home and is being treated with Tamiflu, as is the rest of the family. Other close contacts had also been treated and followed up, Dr McGrath said.

The second confirmed case was an Auckland student who returned to New Zealand from Los Angeles on April 25 on the same flight as the party from Rangitoto College in Auckland which first sparked the swine flu alert in New Zealand.

Dr McGrath said the student was treated with Tamiflu and was now well and out of isolation.

The other four confirmed cases were from the Rangitoto College party, which had been to Mexico before returning home on April 25 on a flight via Los Angeles.

They were put into quarantine, as were all members of the party. All are now clear of the disease and all the students returned to Rangitoto College school today.

Dr McGrath said that as of noon today there were 69 suspected cases, down 20 from yesterday, and 335 people in isolation or quarantine who are being treated with Tamiflu, down by 25 since yesterday afternoon.

These were people who had developed symptoms of influenza within seven days of having been in Mexico or the United States or were close contacts of cases that have flu-like symptoms.

Dr McGrath said there was still no evidence the virus was being transmitted in the community.

"That means that to date, all of the cases have recently returned from travelling in affected areas or been a close contact of a case."

Health Ministry deputy director of public health Darren Hunt emphasised today there was still a chance the virus could keep mutating and be a threat.

Dr Hunt said remaining vigilant was particularly important as New Zealand was headed into the traditional winter flu season.

"Certainly, going into the winter flu season we don't want an additional load of more influenza in the country circulating.

"We also don't have a perfect handle on what this new virus is like yet, and so we are making a lot of effort to ensure there is no community transmission of it," he said.

"Keep it out of the community just in case the virus does change and become more severe."

Prime Minister John Key said today the Government had not over-reacted to swine flu.

"You can't sit back when there's a potential pandemic and do nothing," he told Newstalk ZB.

"The Government put its pandemic plan into action, it was a good plan and it was well thought-through."

Meanwhile, a New Zealand man placed under observation at a hospital on the Malaysian resort island of Penang has been cleared of swine flu, reports said today.

The 45-year old man, who is married to a Malaysian and arrived in the country on April 25, underwent testing after complaining of fever and body aches.

A total of 18 countries have reported 900 cases of human swine flu infections as of 4pm, according to the World Health Organisation (WHO). There had been 20 deaths, 19 in Mexico and one in the United States.

The disease remained at alert level five on the WHO scale, one step away from its highest level.