New Zealand has now recorded more than 70 cases, up from 35 on Friday night.
The virus is now spreading in the community, and not just among people coming into contact with overseas travellers.
The new cases include 14 in the Samoan community in Christchurch.
Health officials believed those cases had been contained but advised Samoans affected not to attend church.
Canterbury medical officer of health Alistair Humphrey said the situation was worsening.
"We think there is going to be cases all over the country and we have certainly had a cluster," he told Radio New Zealand.
"It is gathering pace and we can expect more cases in the days and weeks ahead."
A group of 40 young travellers and their Kiwi Experience bus driver have been quarantined on the West Coast of the South Island after a female passenger tested positive for swine flu.
The development of a swine flu vaccine is expected soon, possibly even in the next month.
US company Baxter International said its Influenza A (H1N1) flu pandemic vaccine could be ready for commercial use next month, The New Zealand Herald reported.
Swiss drugmaker Novartis AG said its vaccine should be available ahead of schedule by September or October.
Wellington health officials have set up a specialist swine flu assessment centre at Wellington Hospital and other DHBs are likely to do the same.
"It diverts people away who may have flu symptoms from hospital and emergency departments and GP clinics," Health Minister Tony Ryall said.
Students at two high schools in Auckland and Christchurch and the police training college in Porirua have being quarantined.
Fifty students and teachers at Burnside High School in Christchurch had been quarantined after a 13-year-old boy attended school with symptoms.
His four-year-old brother attended Tino e Tasi Pre-School with flu symptoms and nine other preschoolers there had since tested positive.
In Auckland, all year 12 students at Westlake Girls High School have been ordered to stay home for the week after a classmate was confirmed with the virus.
Mr Ryall said there was no need for alarm, and that more cases should be expected nationwide.
"We are working to contain the spread as much as possible."
It was likely there would be further partial or full school closures, he warned.
Those who believed they had the flu -- swine or seasonal -- could do their bit to slow the spread by being sensible; anyone with symptoms should not go to school or work, and nor should they just turn up at a medical centre.
"I don't think your work mates or your school mates would be happy if you're spreading it around," Mr Ryall told NZPA.
"(And) you don't want to put people with flu symptoms in with a whole lot of other people turning up at GP clinics.
"You can imagine what it would be like if everyone with flu symptoms turned up at the hospital."
Health officials were also hammering home the need for people who suspect they have the flu to seek medical advice over the phone.
The Ministry of Health has moved its response to phase 6.2 which means restrictions could be placed on public gatherings and a state of emergency could be declared. It is the last phase before code red.
It advised that people who had travelled overseas but were well did not need to be routinely excluded from school or work. However, if they had flu symptoms within seven days they should call their doctor or Healthline (0800 611 116), and not go to school or work.
It was not necessary to cancel or postpone overseas travel, it advised.
"In most cases, people with influenza can safely recover at home and will not need to see their GP or emergency clinic.
"However, people should seek medical advice when necessary, especially if their condition worsens. Seeking medical advice is particularly important for people with underlying medical problems who are at higher risk of complications from influenza."
