This paper reports on an auditory analysis of the historical development of raised and fronted TRAP and DRESS vowels, and centralised KIT vowel in New Zealand English (NZE). For the sake of simplicity, three words from Wells's lexical sets (1982) are used to refer to these vowels. We aim to prove that the realisation of the short front vowels in NZE is not the result of a single factor, but two competing hypotheses have had important roles in this process: new dialect formation and a vowel chain shift. An empirical investigation is carried out regarding a one-hundred-year-long period which considers speech samples of ten male New Zealanders born between 1890 and 1990. The results show that raised TRAP and DRESS originated from England and this finding is supported by the theory of new-dialect formation; they remained high and continued raising as the first steps of a vowel chain shift, while in England they lowered later as an innovation. Thus, the realisation of these vowels is conservative in New Zealand English. Later, DRESS raising triggered KIT centralisation, which was a twentieth-century innovation. Based on the results, it is also proven that it is a push chain consisting of three sequential steps. Furthermore, it is demonstrated that DRESS is still raising, therefore, the vowel chain shift is still in progress. [ABSTRACT FROM AUTHOR]