In the wake of a horrific terror attack in central London that left four dead and almost 40 injured, experts have warned that ISIS jihadists could attack Sydney next.

In a savage assault on London's Parliament, a suspected Islamic State extremist mowed down pedestrians on Westminster Bridge before being shot by officers.

Heavily-armed officers were deployed to guard federal buildings in Australia's capital city in response, with fears similar lone wolf attackers might target Canberra.

'We're making sure that all contingencies are prepared for, but the fact of the matter is some of these things just cannot be preempted,' Counter Terrorism minister David Elliott told 7 News.

In the wake of a horrific terrorist attack in London, experts have warned that ISIS jihadists could attack Sydney next

Heavily-armed officers were deployed to guard federal buildings in Australia's capital city in response after Canberra was placed on high alert

A total of 40 people were injured when the attacker drove a rented Hyundai (pictured after it crashed) down the pavement on Westminster Bridge, plowing into pedestrians

According to reports by 7 and 9 News, 'within months' every front level police officer will be issued a M4 Carbine assault rifle to combat the rising terror threat.

Nick O'Brien, a count terrorism professor from Charles Sturt University, told 9 News that Australia's 'opponents don't like the fact we live in a democracy'.

'All parliaments are a target,' he said.

Other security experts pointed out the high incidence of vehicle-ramming terrorist attacks in recent times, suggesting heightened gutters and bollards in the CBD's.

Gavin Queit, director of a specialist security company based in Melbourne, said bollards were a good way to minimise the likelihood and danger of a vehicle attack.

His company GK Solutions was recently hired to install protective bollards outside a new police station in the heart of Melbourne.

Armed police are pictured on patrol at Parliament House in Canberra, which is on high alert

Gavin Queit, director of a specialist security company based in Melbourne, said bollards were a good way to minimise the likelihood and danger of a vehicle attack

Carmage after the horrific terror attack near London's Houses of Parliament that has left at least five people dead. Pictured, emergency services at the scene

'If you think about a major intersection in Melbourne at lunchtime, people crossing any of the major intersections and cars are waiting opposite and you can't impede those cars,' Mr Quieit admitted to the Sydney Morning Herald.

Neil Fergus from Intelligent Risks told 9 News that terrorist attacks like the latest one in London had the possibility of inspiring other like-minded people.

'There are other parties out there, some of whom are mentally deranged, some of whom are inspired by jihadism, some of whom are a combination of both, who might think that this is something that they might think with give their meaningless lives something,' he said.

An Islamic State propaganda magazine published online late last year implored deranged terrorists to perform horrific attacks on their own.

'Kill them on the streets of Brunswick, Broadmeadows, Bankstown, and Bondi. Kill them at the MCG, the SCG, the Opera House, and even in their backyards,' the article read.

'Stab them, shoot them, poison them, and run them down with your vehicles.

'Kill them wherever you find them until the hollowness of their arrogance is filled with terror and they find themselves on their knees with their backs broken under the weight of regret for having waged a war against the believers, and by Allah's will, and then through your sacrifices, this (community of Muslims) will be victorious.'

An Islamic State propaganda magazine published online late last year implored deranged terrorists to perform horrific attacks on their own. Pictured, investigators at the scene on Westminster Bridge after London terror attack

After arresting a Sydney teenager over a suspected terror plot last year, NSW Deputy Police Commissioner Catherine Burn spoke of the risks of youth radicalisation.

'What is concerning is that we are still seeing people who want to do an attack in our country. We are still seeing people planning and preparing for such attacks and unfortunately that group of people are getting younger and younger and, as we all know, youth are vulnerable particularly around the radicalisation,' she said.

'The really important thing is that we can't do this alone, police cannot do this alone.'

'We all have to work together, whether it's family, schools or other community groups, we all have to work together because we can't be in everyone's bedroom, we can't be in everyone's lounge room.'