WELLINGTON (New Zealand) - NEW Zealand recorded another case of swine flu Thursday as health officials warned of the growing difficulty of keeping the illness out of the country.

The new confirmed case, a passenger on a flight that arrived from North America on Saturday, takes to 11 the tally of confirmed cases since an outbreak of the infection in late April, according to Darren Hunt, deputy director of public health.

The passenger, close contacts and other nearby passengers in the aeroplane have been isolated at home and are being treated with the antiviral drug Tamiflu.

Mr Hunt said the 'sudden increase' in confirmed swine flu cases in Australia and continuing rise in cases notified to the World Health Organisation meant it was 'increasingly difficult to keep influenza A (H1N1) out of New Zealand'.

New Zealand, the first nation in the Asia-Pacific region to record confirmed swine flu infections - all of them in people who had contracted it overseas - so far has prevented the illness from spreading.

It has imposed isolation on all suspected cases of swine flu and posted medical teams at its international airports since late April to assess travellers.

The total of probable cases nationally remains at 10, Mr Hunt said, and there are 66 suspected cases. As people with flu symptoms arrive from affected countries they are isolated and treated with antiviral drugs. -- AP