Melbourne has had its first practice run of a new loudspeaker emergency warning system which will boom through city streets during terror attacks.
The speaker system will be used during "class-three" emergencies which include sieges, riots, an active armed shooter or vehicle attacks and is managed by Victoria Police.
"That signal will go out and will alert the public and say 'listen, pay attention - something is happening'," acting Chief Commissioner Shane Patton said on Thursday.
There are four possible messages, either warning people to move to an area, leave an area, stay inside or seek shelter, he added.
The speakers were tested briefly on Thursday to show the public how they would work.
Once the emergency is over, a message will let people know, Mr Patton said.
However, the acting commissioner was not able to specify how long it would take to get emergency broadcasts on air.
The broadcasts will only be in English but the message will be clear for tourists and those visiting to Melbourne that an emergency was under way, Police Minister Lisa Neville told reporters.
"People may not understand English or the audible message but they will still get and understand the universal warning signal," Ms Neville said.
She said the warning system was just one way people would be alerted, along with mobile phone text messaging, social media posts and police on the ground.
Sixty-five speaker sets were installed at sites including Federation Square, Flinders Street Station and the Bourke Street mall, with more than 90 sites to be completed by the end of 2018.
Sydney has had emergency speakers in place since before the 2007 APEC meeting and other cities around the world use similar warning systems.
