Gough Whitlam, Australia's 21st prime minister, has been lauded at a memorial service in Sydney as a giant of politics and a man who devoted his talents to public service.

Sydney's Town Hall and many of the streets surrounding it overflowed with people wanting to be a part of the memorial service for Mr Whitlam, who died at the age of 98 on October 21.

There were cheers, and some jeers, for the six former prime ministers and current leader Tony Abbott as they filed into the hall to join the capacity crowd of almost 2,000.

"Gough chose this venue," said master of ceremonies Kerry O'Brien. "Of course he did. The people's hall. But it wasn't his first choice. His first choice was to have a funeral pyre in the Senate.

"Big man, big heart, big vision, big hurdles, big flaws, big outcomes, a big life dedicated to public service."

The service was also beamed live into Melbourne's Federation Square and to Cabramatta in Mr Whitlam's former western Sydney electorate.

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There were cheers as Indigenous leader Noel Pearson listed Mr Whitlam's achievements while in office.

"My signal honour today, on behalf of more people than I could ever know, is to express our immense gratitude for the public service of this old man," Mr Pearson said.

"We were at last free from those discriminations that humiliated and estranged our people."

Other speakers included Academy Award-winning actor Cate Blanchett, Mr Whitlam's speechwriter Graham Freudenberg, Labor senator John Faulkner and Antony Whitlam QC, Mr Whitlam's eldest son.

"He touches us in our day-to-day lives, in the way we think about Australia, in the way we see the world," Mr Freudenberg said.

"He touches, still, the millions who share his vision for a more equal Australia, a more independent, inclusive, generous and tolerant Australia, a nation confident of its future in our region and the world."

Blanchett said Mr Whitlam's reforms, including free tertiary education and health care, helped her pursue a career as an actor.

"I was but three when he passed by, but I shall be grateful till the day I die," she said.

"The effect on the geo-cultural political map of Australia made by Gough Whitlam is so vast that wherever you stick a pin in you get a wealth of Gough's legacy."

Prime Minister Tony Abbott, centre, with former prime ministers Malcolm Fraser, Julia Gillard, Bob Hawke, John Howard, Kevin Rudd and Paul Keating at the state memorial for Gough Whitlam. ( AAP: Dan Himbrechts )

The Sydney Philharmonic Choir and the Sydney Symphony Orchestra provided music throughout the service, while Paul Kelly and Kev Carmody performed From Little Things Big Things Grow, a song that tells the story of Gurindji man and Aboriginal rights activist Vincent Lingari and the creation of the Aboriginal Land Rights Act in 1976.

The Gurindji people have never forgotten the man they call Kulum Whitlam, who returned their traditional lands in what became known as the Wave Hill hand-back.

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A group of Gurindji people travelled to Sydney from their traditional home, about 800 kilometres south of Darwin, for the service.

Groups gathered outside the hall and watched the broadcast of the service at other locations, including Cabramatta, in Mr Whitlam's former seat of Werriwa in Sydney's west.

Mr Whitlam was the member for Werriwa for 26 years, after serving in the Royal Australian Air Force during World War II.

One mourner outside the hall wore a T-shirt with Whitlam's famous slogan from the 1972 federal election campaign, "It's Time".

Mr Whitlam left a legacy of unprecedented and unmatched change in Australian politics, but he is perhaps most remembered for his part in the constitutional crisis of 1975 known as The Dismissal.

Mourner Chris Foran said he attended to pay tribute to Mr Whitlam's legacy.

"I don't think we'll see another person like that, as a leader of this country, he was just one in a million," he said.

More than 100 people also gathered at Old Parliament House in Canberra to pay their respects.

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There was laughter, applause and some tears as the group watched a live broadcast of the national service.

Christopher Chenoweth reflected on the significance of watching the service at Old Parliament House, near the halls of power during Mr Whitlam's time as prime minister.

"He made changes that could never be turned back, he made mistakes, he had some extraordinary characters in his ministry, but it was a revolutionary time in Australia I believe," he said.

A large crowd outside Sydney Town Hall watches a screen televising the memorial service for former prime minister Gough Whitlam. ( Instagram: thech3fkid )

'A great man with a great legacy'

Authorities struggled to accommodate the crowds that gathered for the service.

About 6,000 people registered to attend, but there were only 1,000 general public seats, which were allocated on a first-come, first-served basis.

Max McCleod, from Corrimal in northern Wollongong, became emotional after being told he could not get into the service.

"I got out of bed at five o'clock this morning, where I live at Corrimal," he said.

"I caught the six o'clock bus and I've come all the way in here and I can't see the man I know."

Ahead of the memorial, Mr Shorten told Channel Seven that Mr Whitlam was a great man with a great legacy.

"It's sad because a great Australian has left us," Mr Shorten said.

"But it's also a happy day because we recognise that he was a politician, unlike many others, who not only served the nation, but he changed Australia for the better," he said.