Otago and Southland medical officer of health Dr Marion Poore said over the past week Public Health South had managed six suspected cases of swine flu (influenza A H1N1).
Results in last night revealed four of those cases were negative, and results on two more cases were expected tonight.
All the people involved were either tourists or New Zealanders returning home. None had arrived via Dunedin or Queenstown international airports, she said.
For the past six weeks, Public Health South staff and nurses have met all international flights to monitor passengers and would continue to do so, she said.
A surge in the number of Australian cases meant "we anticipate a surge of cases in both primary and secondary healthcare facilities in the coming weeks and are continuing to plan for this across Otago and Southland".
While it appeared the risk of human-to-human transmission was growing "there is no evidence this is happening in New Zealand".
The number of confirmed cases of swine flu increased by one yesterday to 11, following the arrival in Auckland of an infected person from North America.
The cumulative total of probable cases remained unchanged at 10, and there were now 66 suspected cases, up from 51 on Wednesday, the ministry said.
Sixty-three people were in isolation or quarantine and being treated with Tamiflu, up from 54 since Wednesday.
"We are watching with concern the rapid increase in the number of confirmed cases in Australia, particularly in the state of Victoria and some Melbourne schools," said Darren Hunt, deputy director of public health.
"The continuing rise in the number of overseas cases notified to the World Health Organisation and the sudden increase in the number of confirmed cases in our closest neighbour make it increasingly difficult to keep influenza A H1N1 out of New Zealand."
The ministry is launching a campaign this weekend to increase awareness about how to keep swine flu at bay and how to prepare for its likely spread in the country.
Health officials have recommended people stock up on three to five days' worth of food and any medicines required.
Anyone showing symptoms should stay home and contact their doctor by phone, rather than risk infecting others.
As of Wednesday, 66 countries had officially reported 19,273 cases of swine flu, including 117 deaths, the World Health Organisation said.
In Australia, the number of affected people was doubling every two days and reached 502 confirmed cases on Wednesday.
