Background A novel coronavirus first reported in Wuhan City in China in 2019 (COVID-19) developed into a global pandemic throughout 2020. Many countries around the world implemented strict social distancing policies to curb the spread of the virus. In this study we aimed to examine potential change in mental/physical health and social relationships during a highly restrictive COVID-19 lockdown period in Australia during April 2020. Methods Our survey (n=1,599) included questions about concerns, social behaviour, perceived change in relationship quality, social media use, frequency of exercise, physical health, and mental health during COVID-19 lockdown (April, 2020). Results When estimating their mental health for the previous year 13% of participants reported more negative than positive emotion, whereas this increased to 41% when participants reflected on their time during COVID-19 lockdown. A substantial proportion (39-54%) of participants reported deterioration in mental health, physical health, financial situation, and work productivity. However, most of these participants reported 'somewhat' rather than 'a lot' of deterioration, and many others reported 'no change' (40-50%) or even 'improvement' (6-17%). Even less impact was apparent for social relationships (68% reported 'no change') as participants compensated for decreased face-to-face interaction via increased technology-mediated interaction. Conclusions The psychological toll of COVID-19 on Australians may not have been as large as other parts of the world with greater infection rates. Our findings highlight how technology-mediated communication can allow people to adequately maintain social relationships during an extreme lockdown event.