ObjectivePublic cooperation to practise preventive health behaviours is essential to manage the transmission of infectious diseases such as COVID-19. We aimed to investigate beliefs about COVID-19 diagnosis, transmission and prevention that have the potential to impact the uptake of recommended public health strategies.DesignAn online cross-sectional survey.ParticipantsA national sample of 1500 Australian adults with representative quotas for age and gender provided by an online panel provider.Main outcome measureProportion of participants with correct/incorrect knowledge of COVID-19 preventive behaviours and reasons for misconceptions.ResultsOf the 1802 potential participants contacted, 289 did not qualify, 13 declined and 1500 participated in the survey (response rate 83%). Most participants correctly identified ‘washing your hands regularly with soap and water’ (92%) and ‘staying at least 1.5 m away from others’ (90%) could help prevent COVID-19. Over 40% (incorrectly) considered wearing gloves outside of the home would prevent them from contracting COVID-19. Views about face masks were divided. Only 66% of participants correctly identified that ‘regular use of antibiotics’ would not prevent COVID-19.Most participants (90%) identified ‘fever, fatigue and cough’ as indicators of COVID-19. However, 42% of participants thought that being unable to ‘hold your breath for 10 s without coughing’ was an indicator of having the virus. The most frequently reported sources of COVID-19 information were commercial television channels (56%), the Australian Broadcasting Corporation (43%) and the Australian Government COVID-19 information app (31%).ConclusionsPublic messaging about hand hygiene and physical distancing to prevent transmission appears to have been effective. However, there are clear, identified barriers for many individuals that have the potential to impede uptake or maintenance of these behaviours in the long term. We need to develop public health messages that harness these barriers to improve future cooperation. Ensuring adherence to these interventions is critical.