A union flag was set on fire by protesters while Australia marked a national day of mourning for the late Queen.

A memorial service to celebrate the life of Her Majesty was held in Canberra on Thursday – a “one-off” public holiday announced by the prime minister after her death – as anti-monarchy demonstrations were held in Melbourne, Sydney, Brisbane, Adelaide and the nation’s capital.

Prior to the memorial service at Canberra’s Parliament House, footage was shared on social media of the union flag being burned at a park in Melbourne – the starting point for a lunchtime Abolish the Monarchy march.

A video was also shared by a Australian Broadcasting Corporation (ABC) journalist of an Australian flag being set on fire in Brisbane as crowds chanted “always was, always will be Aboriginal land”.

Prime minister Anthony Albanese and governor-general David Hurley, who had only recently returned from the Queen’s funeral, were joined in Canberra by state and territory leaders, ministers, former ministers, ambassadors, chief justices and former governor-generals.

Following a minute’s silence and the singing of the national anthem Advance Australia Fair, Mr Hurley called the day of mourning one of sadness but “also a day of reflection”. He went on to acknowledge that the country’s First Nations people have been “shaped by the colonial history”.

“In considering the unifying role Her Majesty played, I’d acknowledge that her passing has prompted different reactions for some in our community. I’m conscious to respect that many First Nations Australians shaped by the colonial history have brought a reconciliation journey. That is a journey we as a nation must complete,” the governor-general told mourners.

Her (Majesty's) passing has prompted different reactions for some in our community. I’m conscious to respect that many First Nations Australians shaped by the colonial history have brought a reconciliation journey.

“And so to her legacy for us in Australia, I have found myself asking whether the unparalleled reaction of the last 13 days has been just a moment in time, a unique reaction driven by Her Majesty’s remarkable life, longevity, and service, or is there a greater lesson to be drawn? I’d suggest that a lesson for us can be found by being both reflective and prospective in our considerations, to look back and admire and to look ahead and contemplate.”

In his speech, Mr Albanese said the Queen had sought to understand Australia during her 16 trips to the nation during her 70-year reign.

“Monuments to the Queen dot our landscape. The name of Elizabeth lives in nearly every city and town. Perhaps the greatest tribute we can offer her family and her memory is not a marble statue or a metal plaque. It is a renewed embrace of service to community. A truer understanding of our duty to others. A stronger commitment to respect for all,” the prime minister said.

“This would be a most fitting memorial, to a magnificent life of service to others. May Her Majesty Queen Elizabeth II rest in eternal peace.”

Meanwhile, organisers of the Melbourne rally, which included Warriors of the Aboriginal Resistance (WAR) and Fighting in Solidarity Towards Treaties group (FISTT), called for the abolition of the monarchy and an end to “racist, colonial imperialism” which stole from Aboriginal and Torres Strait Islander peoples.

“While they mourn the Queen, we mourn everything her regime stole from us: our children, our land, our loved ones’ lives, our sacred sites, our histories,” WAR said in a statement.

“We stand against racist colonial imperialism and its ongoing effects on us as Aboriginal and Torres Strait Islander peoples.

“We stand in solidarity and rage with other peoples across the world who have been oppressed, murdered, enslaved and vilified under the British colonial enterprise. We do not want to be a part of the Stolen(common)Wealth.”

FISTT spokesperson and New South Wales Greens Upper House candidate Lynda-June Coe called the sudden declaration of a day of mourning for the late monarch “a real insult to First Nations people”.

The Wiradjuri and Badu Island woman told the ABC that since the death of the Queen, Indigenous peoples’ “responses and experiences to colonisation and dispossession” had been silenced and erased.

“Our mob have been calling for our Day of Mourning to be recognised for over 80 years, since 1938,” she said. “It really does show that there are two sides of this story and ours unfortunately continues to be silenced and erased completely.”

In Adelaide, a protester was ejected from Government House for holding a sign and writing “Abolish the monarchy” in one of the Queen’s condolence books. Footage shared by 7News Adelaide showed the man being escorted from the scene by three police officers.

Despite significant pressure to do so throughout Australia’s recent history, no treaty has been negotiated between First Nations peoples. Australia is the only ex-British nation that has not ratified a treaty with its Indigenous peoples – which would require the government to legitimise Aboriginal nations as separate to the nation of Australia.