This study examines news and audience polarisation in the context of the Australian referendum for the establishment of an Indigenous Voice to Parliament. The political leaning of news content is a critical influence on societal polarisation, shaping our understanding of social reality and impacting public discourse. We employ a large-scale dataset and computational content analysis to explore the speakers and their rhetoric featured in news content, in order to investigate differences in coverage choices between news outlets during the referendum campaign. Our study conceptualises and measures coverage polarisation in news content across a selection of the major Australian news outlets, thereby assessing the ability of contemporary news to inform, represent, and serve its intended publics. Through an analysis of news coverage throughout the referendum campaign, this enables a longitudinal diagnosis of news polarisation levels. Furthermore, we investigate links between news content polarisation and polarisation in public discourse on Twitter and Facebook that engages with such content. The insights gained from this research have implications both for scholarship in media and political studies and for the practice of journalism. We provide insights into the referendum coverage decisions of leading Australian news outlets and identify potential feedback loops of polarisation between news content, journalists, and their social media audiences.