NSW teen 'planned attack and Syria trip'

The Attorney-General has reassured Australians about the resourcing of counter-terrorism authorities after the arrest of a terrorism suspect in Sydney.

Tamim Khaja being arrested by police at Parramatta Source: NSW Police

A Sydney teenager whose alleged bid to join extremists in Syria was thwarted earlier this year is now in police custody accused of planning an imminent lone-wolf terror attack in Australia.

The 18-year-old was allegedly in the process of acquiring a gun and was scouting for targets in Sydney that involved buildings representing authority.

The teenager has been named by media outlets as Tamim Khaja, a former student at Epping Boys High School.

He was arrested in Macquarie Park in Sydney's northwest on Tuesday morning in a joint Australian Federal Police (AFP) and NSW Police operation. AFP Acting Deputy Commissioner Neil Gaughan said it's believed the teen was acting alone.

"We have taken swift action to ensure the safety of the community and we are satisfied that any threat to the community posed by the individual has been mitigated," Mr Gaughan told reporters on Tuesday.

The man has been under surveillance since he tried to board an international flight from Sydney Airport in February, but was stopped because his passport was cancelled.

(Supplied: NSW Police) Source: NSW Police.

Attorney-General George Brandis said authorities had not acted until relatively late so more evidence could be gathered.

The man was "in the process" of acquiring a weapon, he told reporters in Brisbane.

"The judgment of the police was that he was intending to put it to use imminently," Senator Brandis said.

It was the ninth time since the terrorism alert level was heightened in September 2014 that authorities had thwarted such a plot, he said.

Last month, a 16-year-old western Sydney boy was arrested on the eve of Anzac Day accused of trying to source a gun for an April 25 terror attack.

The man arrested on Tuesday is expected to face Parramatta Local Court on Wednesday charged with one count of planning a terrorism attack and one of preparing for foreign incursions.

NSW arrest 'not connected to Victoria raids'

The arrest coincided with police raids on properties in Melbourne's northern and north-western suburbs.

Police stress the raids in Melbourne are in no way connected with the arrest made this morning in Sydney.

The five Victorian men have been charged with making preparations to enter a foreign country to engage in hostile activities, but federal police say more charges could follow.

The accused are being extradited to Melbourne to face the Magistrates court on Thursday.