The statue of the British explorer can be seen being sawed at the ankles by two people, and another hooded figure spray-painting “The colony will fall,” on its plinth on Wednesday, 24 January.
A statue of Queen Victoria was also defaced and covered in red paint. Members then stood in front of the monument with a banner saying “Land Back” with the Australian Aboriginal flag alongside it.
“Several people were seen loitering in the area around the time of the incident,” said Victoria Police, who are investigating and have yet to make any arrests.
Victoria state Premier, Jacinta Allen, said: “This sort of vandalism has no place in our community,” and confirmed the statue will be restored.