Notorious Islamic preacher Musa Cerantonio is among five men arrested in far north Queensland over an alleged plan to take a boat to Indonesia and join the Islamic State (IS) terror group.

Key points: Police allege the men were trying to get to Syria via Indonesia

Police allege the men were trying to get to Syria via Indonesia They are being held on suspicion of foreign incursion offences

They are being held on suspicion of foreign incursion offences Police said they had been investigating the men "for weeks"

Shayden Thorne, the brother of another hardline Islamist, Junaid Thorne, was also arrested.

Also in custody is Kadir Kaya, who last year told a Melbourne radio station he wanted to leave Australia because he felt Muslims were not welcome, but could not because the authorities had confiscated his passport.

Police arrested the men on Tuesday as they were towing a boat towards Cape York, in far north Queensland.

They are being held on suspicion of foreign incursion offences.

Police would not disclose how long ago the men travelled from Melbourne to northern Australia but believe they were intending to travel through Indonesia and the Philippines to Syria.

AFP Deputy Commissioner Neil Gaughan said the men, aged from 21 to 33 years old, were "very committed" to leave the country after previously having their passports cancelled.

"The fact that they'd gone all the way from Melbourne, all the way to far north Queensland, indicates that these people were extremely committed in ... their attempt to leave the country," he said.

Victoria Police Deputy Commissioner Shane Patton said police would be considering charges after the men were questioned.

"We have a requirement to ensure that people can't get offshore to go and fight in other countries, can't get offshore to become hardened terrorists and come back here and pose a risk," he said.

"If disruption means ultimately we don't get sufficient evidence so we can charge them, we'll accept that risk."

Police said they executed eight warrants in Victoria and one in Queensland after the arrests to gather evidence.

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AFP allege the men purchased the boat in Melbourne before travelling to Queensland.

Police said they had been investigating the men "for weeks" and there was no domestic terrorism threat arising from the investigation.

Attorney-General George Brandis said it was a unique situation.

"This is the first attempt to leave Australia by vessel of which we are aware," he said.

"I can't rule out the possibility that there may be others but this is the first attempt to leave Australia by vessel of which we are aware."

The ABC understands this is the boat the men allegedly planned to take to Indonesia. ( ABC News )

The boat seized by police is an Australian made Fraser 7 with an offshore hull designed for deep sea fishing.

The model is popular with marlin fisherman and can sell on the second-hand market for up to $70,000, although the version allegedly towed to Queensland by the men appears to be at least three decades old.

A second-hand boat dealer who did not want to be named said the vessel could make it to Indonesia if conditions were calm.

Preacher kept 'low profile' after deportation to Australia

Mr Cerantonio was born into an Italian family in Melbourne's western suburbs, but converted to Islam at the age of 17.

Sorry, this video has expired Federal Police detail arrest of 5 Melbourne men over alleged plan to take boat to join Islamic State

A few years ago, he was one of the most popular and influential online preachers supporting the jihad in Iraq and Syria.

In 2014 he was arrested on the Philippines island of Cebu after using Twitter to tell his followers that he had travelled to Syria.

The Philippines authorities told the ABC at the time of his arrest that they had acted on information provided to them by the AFP.

He was deported back to Australia after his passport was cancelled but never charged.

Since then Mr Cerantonio has kept a relatively low profile online.

Shayden Thorne was jailed in Saudi Arabia in 2011. He spent three years in prison for possession of terrorism-related materials.

He was granted clemency and deported to Australia in 2014.