In the vowels there are notable differences and it is these differences that make up the New Zealand accent. It differs from PR in the sound of the final vowel in words like city . In RP the two vowels in city are precisely alike. Unstressed vowels all tend to sound alike, with the result that there is little difference between effect and affect . The most noticeable difference is in the short vowels.
Phoneticians classify vowels by the position of the highest point of the tongue.
If you are an RP speaker and say slowly in succession pan , pen , pin , the front of your tongue rises one notch higher each time. New Zealand speakers pronounce the first two of these one notch higher than do RP speakers of the same word . Unless you live in Sydney, pin cannot go much higher in the mouth, for there is not much more room at the top. New Zealand speakers move pin backwards slightly and drop it to something like pun . That is why Australians love to twit New Zealanders about Sudney Brudge .