Friday marks the 110th anniversary of Australian and New Zealand soldiers landing before dawn on Turkish shores at Gallipoli on April 25, 1915, alongside British, French and Indian troops.
More than 8000 Australian soldiers died during the unsuccessful campaign to control the Dardanelles Strait.
Attending the dawn service at the Australian War Memorial in Canberra, Prime Minister Anthony Albanese said it was a day to contemplate the debt today's citizens owed to those who served.
"Each year, we renew our vow to keep the flame of memory burning so brightly that its glow touches the next generation and the generation after that," he said.
Just before the anthems played out, one person in the crowd yelled out "free Palestine" - a reminder that while Australians enjoy relative peace, millions of people still face the deadly consequences of conflicts across the world.
Mr Albanese's political opponent, Peter Dutton, laid a wreath at a dawn service in his electorate of Dickson in Brisbane's northern suburbs, alongside his wife Kirilly.
Dawn services and marches across the nation honoured the enduring contributions of service personnel at Gallipoli and the 110 years since, RSL Australia national president Greg Melick said.
"The Gallipoli campaign was the first major military action involving Australian and New Zealand forces," he said.
"They held their ground against almost impossible odds for eight months in the ravines and gullies of that rugged battleground, suffering terrible casualties.
"They fought with endurance, courage, ingenuity, good humour, and mateship."
Anzac Day, held annually on April 25, recognises the more than 1.5 million Australians who have served in wars and peace operations, including 103,000 who have lost their lives.
Governor-General Sam Mostyn, whose father served in the army for four decades, will be the most senior Australian representative at a dawn service at Gallipoli Cove.
In Melbourne, the solemn air was broken during the dawn service when a small cohort of hecklers - led by a far-right extremist - interrupted Bunurong elder Mark Brown's Welcome to Country.
Shouts of "this is our country" and "we don't have to be welcomed" were soon drowned out by applause from the rest of the crowd.
The interruption was widely condemned, with Veterans' Affairs Minister Matt Keogh describing the behaviour as disgraceful.
"When we come together to commemorate on Anzac Day, we're commemorating some of those soldiers who fell in a war that was fought against that sort of hateful (neo-Nazi) ideology," he told ABC radio.
Meanwhile in Sydney, heavy rain was no deterrent as a large crowd gathered at The Cenotaph in Martin Place at a pre-dawn service.
Anzac Day marches will take place in major cities, while in Perth a gunfire breakfast at Government House Gardens is expected to host about 2000 people.
The day will turn more festive when rousing games of two-up - a pastime for soldiers on the battlefield outlawed for 364 days a year - are played at RSLs and pubs throughout Australia.
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