The New Zealand Flag features, on a royal blue background, a Union Jack in the first quarter and four five-pointed red stars of the Southern Cross on the fly. The stars have white borders. It has been the National flag since 1902.
The New Zealand Flag is the symbol of the realm, government and people of New Zealand. Its royal blue background is reminiscent of the blue sea and clear sky surrounding the country. The stars of the Southern Cross emphasise the country's location in the South Pacific Ocean. The Union Flag gives recognition to the historical foundations and the fact that New Zealand was once a British colony and dominion.
The Australian Flag came into being after the federation of the Australian States into the Commonwealth of Australia on 1 January, 1901. Although selected in 1901 and gazetted in 1903, it was not given Royal assent and adopted as the definitive Australian flag until 1954.
The present Australian flag can be considered to consist of three main elements:
The Union Jack in the upper hoist quadrant or first quarter , denoting Australia's historical links with Great Britain.
The Commonwealth Star or Star of Federation, central in the third quarter or lower hoist, has seven points to denote the six states and the combined territories of the Commonwealth of Australia. The seventh point was added in 1909.
So to sum up the main differences. The New Zealand Flag has 4 red stars (with white borders) to denote the Southern Cross while the Australian Flag has 5 white stars and also has the large white star under the Union Jack.
Finally I must also describe the Australian Aboriginal Flag which was adopted as the symbol of Australian Aboriginal and Torres Strait Island people when it was first flown in 1971. It is a strident 3-colour flag composed of a large central yellow circle imposed on a background of a red lower half and a black upper half; the black represents the Aboriginal people, the yellow the sun as a life force, the red the earth and the blood of the Aboriginal people. It has no official government standing but is becoming widely recognized and acknowledged by the community and is perhaps the only symbol commonly accepted by the diversity of Aboriginal people.