The network of loudspeakers to be rolled out in Melbourne CBD could be harnessed by terrorists to carry out a multiple-phased attack, a security expert says.

And the alarms could perpetuate the irrational fear that Australia is “under siege”, said John Blaxland, Professor of International Security and Intelligence Studies and director of ANU’s Southeast Asia Institute.

Victoria’s Police Minister Lisa Neville announced loudspeakers would be installed at more than 90 sites across the city as part of its counter terrorism plan.

Professor Blaxland said he was concerned by “the prospect of the messages actually contributing to the problem” by herding people together.

“A clever terrorist can actually ­­– and this has been done repeatedly in the Middle East, in Iraq and Afghanistan and elsewhere – to stage a multiple-phased attack,” Prof Blaxland told The New Daily.

“The message might be, stay away from location X – like one of the malls, a particular mall – and it might steer people towards a designated safe spot. The designated safe site itself might be actually vulnerable,” he said, as a hypothetical.

I don’t know who it is who would have the insight and the prescience to know what message to communicate that would actually not feed into a plan that a clever terrorist might actually have laid out. That’s where this becomes potentially quite problematic.”

Jacinta Carroll, Director of National Security Policy at ANU’s Security College, defended the announcement as “appropriate”.

“The experience from terrorist attacks overseas in crowded places shows that educating and communicating with the public saves lives,” Ms Carroll told The New Daily.

“Providing mechanisms for awareness and real-time information to be provided to the public gives control back to the public and limits the ability of terrorists to create panic.”

Prof Blaxland believed the speaker system could reinforce “potentially xenophobic” and reactionary fears.

“It’s basically the government saying, ‘We kind of agree with you that it’s important enough for us to put in the kind of measures that we haven’t seen since World War II.

“We used to have air-raid sirens, now we’ve got terror sirens. I’m uncomfortable with what the implications are.”

He said there was a genuine threat of a terror attack, but that it was important to enforce the right measures.

“One of the tenets of countering violent extremism is the importance of getting the message right, about restraint, about proportionality, and about bearing in mind the ramifications across different community groups in a society.”

Test messages to be broadcast before new year

The system will be tested at State Library on December 28. The public can expect to hear a test message and test Standard Emergency Warning Signal.

Ms Neville said 65 speakers have already been installed, and the remainder would be rolled out by the end of next year.

The speakers are part of the state government’s $10 million CBD security upgrade, including permanent bollards along Bourke Street Mall and increased CCTV coverage.

Victoria Police will decide when the speakers are used and what message is broadcast.

Prof Blaxland said the other measures made sense: “Cameras, understandable; concrete planters, understandable – they are clearly measures that will contribute to mitigating the risk an potentially capturing the perpetrators.

“The loudspeakers though, as I say, it depends on how it’s played out, how it’s used.

“So you want to be careful of not being too clever by half, this may – I get the idea, on one level it sounds noble, on another it sounds potentially deeply flawed.”