On 18 September 2021, police officers clashed with protesters in multiple Australian cities during demonstrations organized to denounce the lockdowns enacted to curb the spread of COVID-19. In Sydney, police officers set up roadblocks in several areas to prevent residents from attending unsanctioned protests. Approximately 100 people attended a rally at Sydney Park. A spokesperson for the local police department stated that about 20 people were arrested on public transportation while on their way to participate in the protest. Police officers arrested at least 32 protesters in the city. Meanwhile in Melbourne, approximately 700 protesters gathered in parts of the city as authorities deployed 2,000 police officers to the central business district and shut down public transportation in an effort to prevent large gatherings. A group of protesters breached a police cordon in the inner suburb of Richmond and marched through the streets, obstructing traffic. Individuals threw rocks and other projectiles toward police officers, who used pepper spray to disperse the crowd. According to authorities, 10 police officers suffered injuries during the violence. At least 235 people were arrested in Melbourne.

Additionally, on 20 September hundreds of union workers gathered outside the Construction, Forestry, Maritime, Mining and Energy Union (CFMEU) headquarters building in central Melbourne to oppose mandatory COVID-19 vaccination rules for the construction industry. Protesters yelled obscenities, smashed windows and threw bottles at union delegates attempting to protect the CFMEU building. Police officers initially blocked nearby streets but did not engage the protesters; however, as the crowd grew larger, police officers used pepper spray and rubber bullets to disperse the demonstrators. A number of people suffered minor injuries during the violence. Following the event, the state government of Victoria ordered the closure of all construction sites in Melbourne and surrounding areas — which are currently subject to lockdown measures — for the next two weeks as of 2359 local time (1359 UTC) on 20 September.