Some of Melbourne's best known locations are being reinforced with concrete bollards after recent terrorism attacks at home and in London.
Victorian Premier Daniel Andrews says the temporary bollards will be placed quickly at Federation Square, Bourke Street Mall and other busy public places to stop unauthorised vehicles entering.
"There's no time to be wasted here," he told reporters on Saturday.
The barriers had already been erected along the northern edge of Federation Square with more expected to be installed across the city in the coming weeks.
"The threat of terror, the threat of hostile vehicle attacks, the threats to public safety are all too real," Mr Andrews said
He said the bollards would later be replaced with street furniture or planter boxes and other features that would be a "little bit less imposing" but the priority was safety.
"It's about doing everything we need to do to keep Victorians safe."
Victoria Police Assistant Commissioner Stephen Leane said the bollards would help bolster security in the CBD but warned there were a "number of vulnerabilities" across the city.
"We understand what they look like and where they are and we will be working our way through them over the next six months to provide safety and safer places for our community," he said.
The announcement comes in the wake of recent terror attacks in London and Manchester as well as Monday's siege at Brighton that left two people dead and three officers injured.
In January six people were killed and dozens were injured in Bourke St when Dimitrious Gargasoulas ran them down in a car massacre.
"We think about London, about other tragic events on the other side of the world and events very close to home," Mr Andrews said.
"We need to be vigilant in all manner of different ways and that's what it's all about."
State opposition leader Matthew Guy said the premier should back mandatory sentencing plans proposed by the Liberals to keep violent offenders in jail and off streets.
"Prevention is better than a cure," he said.
