Other posts using the hashtag focused on Indigenous lore and colonial invasion, and fighting a tyrannical empire.
The building, which was the seat of Australiaâs federal Parliament between 1927 and 1988, is now a popular tourist attraction and houses the Museum of Australian Democracy.
Police in Canberra said protesters had started a fire at the main entrance, following âongoing protest activity at the front of Old Parliament House" over the past two weeks.
âA police investigation into the cause of the fire has commenced,â a spokesperson said. âOld Parliament House will remain closed until further notice.â
The building was evacuated and the blaze quickly extinguished by firefighters, police added.
Prime Minister Scott Morrison said authorities should act swiftly to ensure those responsible faced consequences.
âI am disgusted and appalled by behavior that would see Australians come and set fire to such a symbol of democracy in this country,â he said in a news conference.
Earlier, Michael McCormack, a conservative lawmaker, said protesters were heard chanting âlet it burn.â
âHow disgraceful,â he wrote on Twitter. âAn outrageous attack on our democracy, our history, our sovereignty.â
A spokesperson for the Aboriginal Tent Embassy, a protest camp that has occupied a site outside Old Parliament House for decades, did not immediately respond to a request for comment.
The MMAMV Facebook page shared video of protesters clashing with police at the scene, while local journalist Rachel Baxter tweeted footage of protesters targeting media workers.
MMAMV has organized protests over the past six months in Sydney, Melbourne and other cities around the country, with speakers including far-right politician Pauline Hanson. Its Facebook page shares posts and images critical of vaccination and medications. It also posts about child trafficking concerns and freedom.
The group does not appear to be associated with Indigenous organizations or issues. At Thursdayâs protest, however, some of those present waved the Indigenous flag, wore dot-painting shirts, carried Indigenous instruments and appeared to perform an Indigenous dance in front of the fire.
The building was also forced to close last week because of a fire during a protest, which was reported as an accident.
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