A 20-year-old man has been charged with five offences, including preparing for a terrorist act, after his online activity was investigated by police.

Police said they had carried out a search at a home in the Wheatbelt region where officers allegedly seized firearms, imitation firearms, a ballistic vest, gas masks, and lock-picking equipment. 

WA Police Commissioner Col Blanch told reporters officers allegedly also found  a notebook.

It ‘outlined preparations for a terrorist attack at significant locations, including the WA Police Headquarters, building, Parliament House and places of Muslim faith’, he said.

The raid followed a probe by the WA Joint Counter Terrorism Team into the young man’s online activity, officers said on Friday.

The team included members of state police, Australian Federal Police and the Australian Security Intelligence Organisation.

Following the raid on the Wheatbelt property, the 20-year-old from Bindoon was charged with acting in preparation for a terrorist act.

He was charged with one count of using a carriage service to menace or harass and one count of possessing a prohibited weapon. He is also accused of two firearms offences. 

A 20-year-old man in WA has been charged with five offences, including preparing for a terrorist act, after his online activity was investigated by police (stock image)

The arrest comes just a month after 31-year-old Liam Alexander Hall was accused of throwing a homemade bomb into an Invasion Day rally crowd

The incident has been declared an act of terror – the first in Western Australia’s history 

Premier Roger Cook said on Friday that police allege the man allegedly was motivated by a white supremacist ideology and his plan had been for a ‘mass casualty event’ on a range of public buildings across Perth.

After an appearance at Perth Magistrate’s Court on Friday, the 20-year-old’s bail was refused while the matter is before the court.

Commissioner Blanch said police believe the plot was a confined event and that they do not believe the community is at risk. 

The arrest comes just a month after 31-year-old Liam Alexander Hall was accused of throwing a homemade bomb into an Invasion Day rally crowd.

The incident has been declared an act of terror – the first in Western Australia’s history. 

Thousands of people were evacuated from Forrest Place in Perth’s city centre after police found an object containing volatile chemicals, nails and metal ball bearings.

Magistrate Lynette Dias later lifted a suppression order on Hall’s identity on February 17 after hearing submissions from a commonwealth prosecutor and lawyers for various media outlets.

The matter was adjourned to March 31 after a Commonwealth charge of engaging in a terrorist act was added to two state charges. 

If Hall is found guilty of the terrorism offence, he faces life behind bars.

He is yet to enter pleas to any of the charges, which also include an unlawful act or omission with intent to harm and making or possessing explosives under suspicious circumstances.