Prime Minister Tony Abbott said the advice was not based on knowledge of a specific attack plan but rather a body of evidence that points to the increased likelihood of a terrorist attack in Australia, Xinhua reported.
"Security and intelligence agencies are concerned about the increasing number of Australians working with, connected to, or inspired by terrorist groups such as ISIL (now known as IS or Islamic State), Jabhat al-Nusrah, and Al Qaeda. The threat they pose has been increasing for more than a year," Abbott said in a statement.
First priority of the govt is to ensure the safety and security of its citizens
"The first priority of the government is to ensure the safety and security of its citizens. Raising the alert level to high is designed to increase vigilance and raise awareness in the community."
Abbott said state and territory governments were notified of the decision to raise the threat level and federal and state law enforcement agencies will work to counter the terrorist threat.
"The government is also taking strong action to equip our security agencies and border protection agencies with the resources and powers they need to detect terrorist activities at home and prevent radicalised foreign fighters from returning to Australia," he added.