Prince William and Kate surprise at Australian and New Zealand Army Corps service

The young royals were among tens of thousands who attended events marking Australian and New Zealand Army Corps (ANZAC) Day in Australia and New Zealand, on the 99th anniversary of the ill-fated Gallipoli landings of World War I.

The April 25, 1915 landing of the ANZAC at Gallipoli in modern-day Turkey has become a defining symbol of courage and comradeship for both countries.

Each year thousands attend services to remember the campaign which ultimately took the lives of more than 10,000 Australian and New Zealand servicemen.

"I said to them it means a great deal to our nation that you should honour us by attending the dawn service," Australian War Memorial director Brendan Nelson said.

"...without hesitation they had an immense sense of pride in actually being here. But in the end... it's not about the royals, it's not about the governor general... it's about the men and women we honour."

In Sydney, thousands crammed in Martin Place in the heart of the city for a sombre dawn service ahead of a march through the city expected to feature 20,000 former and current defence personnel.

In New Zealand, tens of thousands of people attended services with a dawn march in Wellington led by returned servicemen and women dressed in exact replicas of the 1914 New Zealand infantry uniforms.

The uniforms were the brainchild of Oscar-winning director Peter Jackson who said he wanted to catch the imagination of young people.

The soldiers performed historical military drills carrying the large Long Tom and Lee Enfield rifles used by New Zealand troops at the start of World War I while two women soldiers wore the uniforms of nurses.

"The Defence Force have been enthusiastic about trying something different this year," Jackson said. "The soldiers got into it, wearing the kit of their forebears."

United States Secretary of State John Kerry also acknowledged the sacrifice of Australian and New Zealand soldiers in war, extending the best wishes of President Barack Obama on the national holiday.

"Today, as all members, past and present, of the defence forces of Australia and New Zealand are honoured, know that the United States stands with you in unwavering support as a true friend and partner," he said.