For 67 years, Walter "Wally" Scott-Smith has been the chief custodian of the Martin Place Cenotaph – and he has never missed a dawn service.

In fact, Mr Scott-Smith has stood guard over the sacred spot for a total of 4355 services, with 65 services being held at the site each year.

The humble 90-year-old from Kingsgrove was on Thursday morning named one of three Anzacs of the Year, the announcement following the dawn service drawing cheers and hearty applause from the 20,000-strong crowd in Martin Place.

Since he began his duties in 1967 after appointment by the RSL, Mr Scott-Smith and his team have tirelessly tended to the sombre memorial - "rain, hail or shine" - cleaning it and arranging the floral tributes, standing guard and providing a friendly face for those who come to pay their respects to the fallen.

One year, Mr Scott-Smith turned up to a dawn service with a drip still in his arm, having a fortnight earlier undergone triple heart bypass surgery.

Doctors said he could not attend, largely because of the drip and dressings had to be changed every six hours, but: "I was determined to make it ... So I turned up, and when the dawn service was over I raced home, had it changed and was back for the sunset service."

An ex-serviceman himself, Mr Scott-Smith said his workplace was quiet, but an "enjoyable place", providing a sanctuary for people to remember "our friends that are not about with us any more".

He said he met some wonderful people, seen people grow up as their faces return year after year.

As dawn broke over Martin Place on the 98th anniversary of the battle of Gallipoli on Thursday, he recalled meeting "one fellow that comes from the country, Junee [in the NSW Riverina], comes and puts a red ribbon on the soldier's right hook".

"One year he brought his mother, the next year his wife, the next year the whole family," Mr Scott-Smith said with a smile.

Earlier, the haunting tones of the Last Post brought tens of thousands of Australians in the centre of Sydney to a solemn and reflective pause on Thursday morning, as traditional Anzac Day commemorations began under clear skies.

An estimated crowd of more than 15,000 began pouring into Martin Place in the early hours of the day, taking up every spare inch around the Cenotaph, from George Street up to Macquarie Street.

Led by Premier Barry O'Farrell, the Lieutenant-Governor, Tom Bathurst QC, and Rear-Admiral Tim Barrett, Commander of the Australian Fleet, the crowd joined in prayer to commemorate the 98th anniversary of the battle of Gallipoli.

"We remember a battle that forged a way of life, we remember the extraordinary cost of war that finally led to peace," said chaplain Richard Quadrio, leading the congregation in prayer.

"We remember that victory is always costly, and remember that evil is always crouching at the door ... Peace can never be taken for granted."

In his address, Admiral Barrett said Gallipoli should be remembered as a momentous day in our nation's history, as it was when our "national identity was forged".

He said Anzac Day is a day of reflection to honour not just those who served and died in the historic battles on the peninsula, but those who have "served and sacrificed so much for us" in war and peacetime every year since.

He called on all Australians to pay a special tribute to the 3000 men and women serving around the world today.

The first official dawn service was held at the Sydney Cenotaph 1927, and today forms an integral part of commemorations around the country.

At exactly 5am, the floodlights that illuminated Martin Place were extinguished for the lone bugler's emotive Last Post.

In the pre-dawn darkness, the crowd of up to 20,000 fell completely silent in symbolic homage to the quiet, peaceful moments before the Anzacs' dawn landing at Gallipoli.

The service concluded with resounding renditions of both the Australian and New Zealand anthems.

With no surviving Anzacs remaining, their children, grandchildren and great-grandchildren were among those who turned out in tribute to their ancestors.