Melbourne's terrorism public alert system will be given its first major trial with sirens and a warning message due to blast across the city.
The "first large-scale testing of the CBD security speaker systems" is scheduled for Tuesday, Victoria Police Assistant Commissioner Stephen Leane told reporters on Monday.
"There are 65 sites across the CDB which will be tested initially as a group and then as a series," he said.
"They will be very loud. Police will be at every site of the speakers. If any member of the public needs reassurance police are there for that purpose."
Mr Leane wanted to tell people involved in the Bourke Street or Flinders Street rampages about the testing to ensure they were in a safe place and had support during the testing.
He also said it was important for the rest of the city not to be alarmed when the sirens rang out.
"We are hoping the system will work most effectively. It is a test, so if we have any problems, it is better to find out (before an emergency)," Mr Leane said.
The siren will ring out from 130 speakers at 65 locations for up to 30 minutes and follows a small public demonstration of the system at one site in December.
Another 60 speakers at 30 more locations across the city are expected to be installed by the end of 2018.