In a war that engulfed the world, the young Anzac nations were the hardest hit, forging an unbreakable brotherhood between them.

Those were the reflections of Prime Minister Tony Abbott and his New Zealand counterpart John Key at the most solemn of the centenary commemorations in Albany, Western Australia, on Saturday – 100 years to the day since the first convoy of troops departed for World War I.

The war to end all wars proved a baptism of fire for the two colonies, Mr Abbott told the thousands of spectators near the spot where those servicemen set sail.

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“The scale of sacrifice and loss was beyond anything imaginable,” Mr Abbott said.

“From a population of under five million (in Australia), 417,000 enlisted.

“61,000 never came home.

“Of Australian men aged 18 to 42, almost one in two served in uniform. Of those who served overseas, almost one in five died on active service.

“It was sacrifice on a stupendous scale and it was a sacrifice shared by our neighbour New Zealand.”

Mr Key said it was the nations’ coming of age.

“As the New Zealanders’ vessels met the Australian vessels, the cheering and counter-cheering, the Maori war cries and the answering cooees would have moved a stoic,” he said.

“Young Australia was welcoming young New Zealand … in the first meeting of those brothers in arms, soon to be known by a glorious name.

“And the very first part of their legend was written here.”

Mr Key said the growing number of people honouring the Anzac legend was testament that their memory would not be forgotten.

“We give thanks to the privileges we enjoy today because of their efforts,” he said.

Navy ships from Australia, New Zealand and Japan then passed through Albany’s Ataturk Channel to commemorate the first Anzac convoy’s departure.

A century ago, almost 30,000 soldiers set sail from King George Sound on Western Australia’s southern coast, and on Saturday, the centenary commemorations culminated in the re-creation of that historic event.

Australian warships HMAS Anzac, HMAS Arunta, HMAS Stuart, HMAS Sirius and the submarine HMAS Rankin were joined by New Zealand ship HMNZS Te Kaha and JDS Kirisame from Japan.

Just before the sail-past was the official opening of the National Anzac Centre.

Visitors to the multimedia museum can follow the story of a single soldier, not knowing until they get to the end of the experience whether that serviceman survived or not.

“It is a lasting reminder of those that fell,” Albany mayor Dennis Wellington told the large crowd of dignitaries at the opening.

Mr Abbott said it was fitting the centre should be at the jumping-off point for the original Anzacs.

“I wonder at the heroism and I tremble at the suffering of our forebears but I marvel at what they’ve done for our country,” he said.