A dozen New Zealand Qualifications Authority (NZQA) staff have been quarantined after a colleague contracted swine flu.

The employee with swine flu worked on level 13 of a central Wellington office building, and was sent home on Friday.

When the diagnosis was confirmed yesterday afternoon NZQA quarantined a dozen people from level 13.

The number of confirmed New Zealand cases of swine flu rose to 19 yesterday, with two new confirmed cases being reported by Wellington's Regional Public Health overnight.

Since then the Canterbury District Health Board has confirmed another case, bringing the number to 20.

Canterbury Medical Officer of Health Dr Alistair Humphrey said the woman was a passenger on a plane that returned from Chile, last Thursday.

He said the woman has the unpleasant symptoms of the flu but is not seriously unwell.

Dr Humphrey said the woman isolated herself from other people and has been given Tamiflu.

"Passengers that were near the woman on the flight to Auckland are being contacted," Dr Humphrey said.

The two swine flu cases confirmed last night arrived in New Zealand on Air New Zealand flight NZ5 from Los Angeles on May 31 and became unwell after travelling together.

Swabs were taken from both on Sunday, and they and their close contacts were being treated with Tamiflu and had been asked to stay at home in isolation.

While numbers of those infected are relatively small, the flu strain is new and people have never been exposed to it, so it was expected to spread quickly.

In its present form, officials believe the virus is unlikely to result in a higher death toll than seasonal flu.

The confirmed cases have occurred in Auckland, Wellington, Christchurch and Hawke's Bay. Most have recovered.

The number of probable cases was 11, up from 10 on Monday, and there were 161 people in isolation or quarantine and being treated with Tamiflu, up from 92 on Monday.

A group of Gisborne Boys' High school students who travelled home from a school trip to Brisbane on Sunday were yesterday isolated at school for the day.

Those with flu symptoms were given Tamiflu and asked to stay at home in isolation. The group includes 16 students, two teachers and a parent.

Worldwide, more than 26,000 cases, including 140 deaths, have been reported in 73 countries. Australia's total has passed 1200 cases, mostly in Victoria, and is rising rapidly.

The World Health Organisation said on Tuesday the spike in Australian cases may push it to announce the first flu pandemic in 41 years.

It also expressed concern about an unusual rise in severe illness from the disease in Canada.

But the WHO's flu chief Keiji Fukuda said the agency wanted to avoid "adverse effects" if it announces a global outbreak of swine flu. Fukuda said people might panic or that governments might take inappropriate actions if WHO declares a pandemic.

In most countries, the new H1N1 virus has triggered only mild illness. But the fact that some of the deaths have occurred in otherwise healthy adults has prompted WHO to classify the outbreak as "moderate" for the time being.

Notifiable diseases

The Government on Monday added swine flu to the list of notifiable diseases.

This allows people who have been in contact with patients who have swine flu to be compulsorily isolated at home, and pupils and teachers who are patients or contacts to be excluded from schools.

These measures are in addition to the general powers of medical officers of health under the Health Act 1956 to isolate people considered at risk of spreading swine flu.

A person who disobeys medical officers' orders faces a $500 fine, plus $50 for each further day of non-compliance.

But it is more likely the officer would invoke the power in section 79 (4) of the act to "detain him, by force if necessary".

Anyone who leaves their specified place of isolation is liable to be "arrested by any officer of the Ministry of Health or by any member of the staff of the hospital or other place of isolation or by any constable, without warrant" and taken to the place of isolation.

As well, medical officers of health gain much wider powers - such as restricting travel, closing businesses and banning meetings - if the Prime Minister issues an epidemic notice, the Minister of Health gives authority or a state of emergency is declared.

Then the penalty for disobeying a medical officer of health's directions rises to a maximum of six months' jail and a fine up to $4000.

The director of public health, Dr Mark Jacobs, said yesterday the Health Ministry's preference was voluntarily compliance and that was working well.

"If we had a problem with that, our fall-back wouldn't be to take them to court and fine them. It would be to enforce isolation, because the purpose of this is public health.

"Public health is not served by fining them."

The preference was to isolate people at home, or at hospital if necessary, he said.

Asked if police cells could be used, he said it was "unlikely but is in theory a possibility."

And he said it was unlikely the powers triggered by ministerial order or emergency declaration would be needed, even if swine flu - influenza, A (H1N1) - spread widely.

* The price of disobedience

$500 fine for refusing to be isolated.

$50 for every day of continued refusal.

Detention by force if necessary.

- With AP