Australia's former parliament building in the capital Canberra was briefly set alight on Thursday by protesters during a demonstration for Aboriginal sovereignty, police said.
No-one was injured in the fire, which engulfed the Old Parliament House's front doors before it was put out.
It follows a fortnight of protest activity at the site, police said.
Protest violence on this scale is rare in Australia, but flare-ups have become more common during the pandemic.
Some of the protesters had identified themselves as part of anti-government and "sovereign citizen" groups, observers said.
Prime Minister Scott Morrison condemned the violence, saying: "This is not how Australia works."
"I am disgusted and appalled by behaviour that would see Australians come and set fire to such a symbol of democracy in this country," he said.
Workers inside the heritage building were quickly evacuated once the fire broke out on Thursday.
The current residents of the building, the Museum of Australian Democracy, had on 20 December shut its doors after indigenous protesters held a "peaceful sit-in".
The museum said it recognised protesters' rights to a peaceful protest. It has not yet addressed Thursday's protest.
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