A man has been charged over a disturbing alleged plot for a “mass casualty” terror attack targeting public buildings in Western Australia.

Police raided the home of Jayson Joseph Michaels, 20, on Thursday and seized a stash of knives, seven rifles and a disturbing manifesto notebook that revealed his alleged plans.

Police also uncovered gas masks, a ballistic vest, lock-picking equipment and imitation firearms at the property in Bindoon, a small farming community in WA’s wheatbelt, north of Perth.

Michaels appeared in Perth Magistrates Court on Friday facing five charges, including acting in preparation for a terrorist act.

WA’s Premier Roger Cook said that the self-radicalised Michaels was allegedly planning to attack the WA parliament, police headquarters and mosques.

“It will be alleged this person was motivated by a white supremacist ideology,” said Cook.

A joint counter-terrorism team began investigating Michaels in January after it received intelligence about encrypted communications concerning white supremacist ideology, anti-Muslim ideology, and antisemitism.

A stash of knives was seized. Photo: WA Police

WA Police Commissioner Col Blanch said investigators also found “abhorrent” conversations about minorities and other races in the messages.

Officers swooped on Michael’s home on Thursday after identifying him as the alleged source.

“We observed and have now seized firearms, imitation firearms, a ballistic vest, gas masks, and lock-picking equipment,” Blanch said.

“Most concerning, there was a notebook that outlined preparations for a terrorist attack at significant locations.”

Firearms and imitation firearms were at the home. Photo: WA Police

It will be alleged that Michaels was acting alone and had written a “concerningly detailed” manifesto outlining plans for an ideologically motivated “extremely serious terrorist attack” involving firearms and explosives.

Officers seized seven rifles from Michael’s property, and police had no intelligence about him before the investigation started.

“The fact that someone can be online and be radicalised so easily, and have no record about their history … that’s what should concern us,” Blanch said.

A box of ammunition was among the weapons. Photo: WA Police

Prime Minister Anthony Albanese said the allegations were “deeply shocking and that Michaels should face the full force of the law.

“As I’ve said many times, we need to take the temperature down. Political leaders have a particular responsibility not to fan the flames of bigotry.

“There is no place in our country for any kind of ­racially or religiously motivated prejudice or hate.”

Photo: WA Police

Authorities continued to investigate the encrypted communications platform, which contained conversations with people from outside Australia sharing white supremacist ideology.

Michaels has also been charged with using a carriage service to menace or harass, possessing a prohibited weapon and two firearms offences.

He was remanded in custody to reappear in the same court on March 23.

-with AAP