Two men have been arrested over alleged links to terrorist groups in Syria, as the federal government considers raising alert levels.
The Queensland arrests involved 180 officers executing nine warrants acting on evidence gathered over a year-long investigation.
Prime Minister Tony Abbott and national security chiefs have been voicing concerns about an estimated 60 Australians fighting in Iraq and Syria and a further 100 providing support from Australia.
US President Barack Obama is set to outline in a major speech on Thursday how a new international coalition will seek to destroy Islamic extremists and deal with the threat of returning foreign fighters.
The Brisbane arrests on Wednesday came as the Victorian and Queensland police chiefs endorsed the suggestion by outgoing ASIO chief David Irvine that the terrorism alert level be raised from medium to high.
Victoria Police Chief Commissioner Ken Lay said the risk of a terrorist attack on home soil, linked to unrest in the Middle East, had reached a new high in the 13 years since the September 11 terror attacks in the US.
"The risks are probably as high as they have been since September 11," he said.
Queensland Police commissioner Ian Stewart said it was the right time to review the threat level, especially with the G20 summit in Brisbane in November.
"But there is no known threat to any industry, or to any site or to any person in Queensland at this particular time," he said.
"However, we would be remiss if we hadn't planned for all contingencies around the G20 summit."
Deputy Prime Minister Warren Truss said it would be a big step to lift the level to high or extreme.
Opposition Leader Bill Shorten said Labor had not been briefed on any changes to the terrorism threat level but had confidence in the national security agencies.
Amid calls to raise the level, airport checks are to be toughened under a plan announced by Immigration Minister Scott Morrison on Wednesday.
"We know there is a very real threat by the death cult that's operating in Iraq and Syria," he said.
The government intends to expand passenger processing and screening systems that it acknowledges could lead to travel delays.
The aim is to stop Australians participating in terrorist activities overseas and identifying those returning from conflicts in places such as Syria and Iraq.
Queensland police have charged a 21-year-old man with preparing for incursions into Syria and he'll also be charged with recruiting fighters to join the conflict.
A 31-year-old man will be charged with providing funds to the Syrian-based terrorist organisation Jabhat al-Nusra.
He'll also be charged with preparing for incursions into Syria.
Australian Federal Police counter-terrorism manager, Assistant Commissioner Neil Gaughan, said the two men were not accused or suspected of planning terrorist acts in Australia.
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