A Captain Cook memorial statue has been sawn off at the ankles and a Queen Victoria monument doused in red paint on the eve of Australia Day.
Police are investigating criminal damage to the Cook statue at Jacka Boulevard, St Kilda, reported about 3.30am on Thursday.
Several people were seen loitering in the area about the time of the incident, police said.
A video posted to Instagram shows a group, with their faces covered, bringing down the statue and spray painting the words "the colony will fall" on the stone plinth.
The same group visits the Queen Victoria memorial at Queen Victoria Gardens and throws red paint over the monument.
Port Phillip Council Mayor Heather Cunsolo said she was disappointed the statue of Captain Cook had been vandalised.
"We understand and acknowledge the complex and diverse views surrounding Australia Day," she said.
"We can't condone, however, the vandalism of a public asset where costs will be ultimately borne by ratepayers."
The Cook statue has been taken away and workers removed the feet from the plinth.
Ms Cunsolo said the council had arranged for security at the monument from Thursday afternoon as a precaution.
The same statue was doused with red paint by protesters in January 2022 as an "invasion day" statement.
A spokesperson for the City of Melbourne said the council was aware of the Queen Victoria memorial vandalism and notified police.
A spray can and red paint tins were seen metres from the statue.
Victorian Premier Jacinta Allan said the government would work with Port Phillip council to repair and reinstate the Cook statue at St Kilda.
"This sort of vandalism really has no place in our community," Ms Allan said.
Opposition Leader John Pesutto said vandalism was "totally unacceptable".
"There's no place for acts of vandalism or any other violent acts against people or property in our community," he said.
"We support the right of people to protest and demonstrate but it must always be done in a peaceful and respectful way."
While January 26 continues to mark a historically significant day commemorating the anniversary of British settlement in 1788, its meaning is becoming increasingly contested.
For a growing portion of the population the day marks the beginning of a colonial history afflicted with discrimination and dispossession of Indigenous peoples, prompting calls to change the date of the national day.
January 26 is alternately observed as a day of mourning for Indigenous Australians, with invasion and survival day protests.
Australia Day wasn't always celebrated on January 26, once a NSW-centric celebration honouring the foundations of its capital city.
Since its official recognition as Australia Day in 1935 and establishment as a public holiday in 1994, January 26 has become synonymous with nationalist festivities.
Rachael Ward, Tara Cosoleto and Vi Truong - AAP