The men are suspected of "potential offenses against the Commonwealth Criminal Code Act, specifically those concerning incursions into foreign countries to engage in hostile activities," according to a joint press release by the Australian Federal Police, Victoria Police and the Queensland Police Service.
As the suspects' passports had been canceled, their only option to leave Australia was by sea. They were found with a seven-meter fiberglass cabin cruiser allegedly bought to make the trip.
These men had purchased a boat in Victoria, and had driven to far north Queensland, where their intention was to depart Australia, according to CNN.
He said that the men had been under investigation for "a number of weeks." Police swooped to arrest them near the northern Queensland city of Cairns.
CNN affiliate Seven News reports that their first likely port of call would have been Indonesia, 3,000 kilometers (1,864 miles) from northern Queensland. Images of the boat's interior obtained by the network show just one plastic-wrapped case of bottled water for the five men.
Victoria Police Deputy Commissioner Shane Patton suggested that the five were committed to joining extremist groups overseas, pointing to Syria as a likely final destination.
"This is a serious attempt by five men, who are of security interest to us, who have had their passports canceled, in attempting to exit Australia, so that they can make their way through boat, and then ultimately, we are investigating the intention to possibly end up in Syria to fight," he said.
He acknowledged that some members of the public may see letting the five "take their chances in the waves" to be the best course of action, but said that authorities cannot allow Australians "to support terrorism anywhere."
He said that if the suspects were to make it to Syria they could come back "battle hardened," highly skilled and further radicalized, representing an even greater threat to Australians.
Authorities have executed nine search warrants in Melbourne and North Queensland to gather evidence for the investigation.