Australia's terror threat level raised from medium to high

Australia's terrorism alert level has been raised from medium to high.

The change announced by Prime Minister Tony Abbott on Friday means a terrorist attack is now considered "likely".

He stressed it did not mean a terrorist attack was imminent.

"We have no specific intelligence of particular plots," he told reporters in Melbourne.

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"What we do have is intelligence that there are people with the intent and the capability to mount attacks."

The move was foreshadowed by ASIO director-general David Irvine earlier this week amid fears Australians returning from the battlefields of Syria and Iraq could pose a danger.

The decision to raise the threat level was based on an accumulation of indicators, Mr Abbott said.

They include the number of Australians in the Middle East fighting with and supporting terrorist groups, those returning from there having fought with terrorist groups and the people in Australia who are known to be supporting these terrorists groups.

Mr Abbott said the increased threat level would not make a difference in the daily lives of the vast majority of Australians.

However, they will notice more security at airports, ports, military bases, government buildings and large public events.

Victoria Police Chief Commissioner Ken Lay says a heightened police presence will be in place at the AFL grand final and the spring racing carnival.

This will include Friday night's semi-final between Geelong and North Melbourne at the MCG.

"People going to the game will definitely see more police," Mr Lay told reporters on Friday.

"This is really just about public reassurance and giving that very high visibility."

Victoria Police will meet throughout the week with the AFL to decide how the remainder of the finals series is policed.

Mr Abbott wants Australians, especially those attending footy finals during the next few weeks, to go about their lives as normal.

"We certainly want people to enjoy the football if their teams are lucky enough to be in the grand final," he said.

"Normal life in Australia can and must go on."

Departing ASIO Chief David Irvine

Mr Irvine, who is stepping down as ASIO head this week, reiterated there were between 60 and 70 Australians fighting for extremist groups like the Islamic State.

But he also emphasised how Australia's security, intelligence and police organisations were out-smarting terrorists.

He denied the decision to raise the threat level was linked to the government's likely support of a US-led coalition that will seek to destroy the extremist Islamic State group in Syria and Iraq.

Mr Irvine said ASIO's decision was based on expert advice provided to it over a long period of time.

"It was taken independently of any decisions that the government might make in relation to interventions or whatever in the Middle East," he said.

Protests target Abbott

Earlier, protesters targeting Prime Minister Tony Abbott have clashed with police at Melbourne University.

Police stopped them from entering a building where Mr Abbott was giving a speech.

The prime minister managed to avoid the protest as he went inside the University of Melbourne building to officially open the Peter Doherty Institute for Infection and Immunity.

He left in a commonwealth car as a handful of shouting protesters chased the vehicle.

Up to 200 demonstrators earlier shouted slogans and called for no cuts to education.

One student said he hurt his lower back as demonstrators chased the car, claiming he was tackled to the ground by police or security personnel as he waved a flag on the road.

Victoria Police said there had been no arrests.

Mr Abbott cancelled a visit to Geelong's Deakin University in May amid nationwide protests against the deregulation of student fees, saying he did not want to inconvenience police and give angry students the chance to riot on national television.

Foreign Minister Julie Bishop was jostled and shoved before having to be ushered by security from Sydney University in May while former Liberal MP Sophie Mirabella was forced to leave the Melbourne University campus under police escort after being accosted by protesters.

Police push back student protesters targeting Prime Minister Tony Abbott at Melbourne University. Photo: AAP

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