Australia's Governor-General, Sir Peter Cosgrove, has praised Queen Elizabeth II as "a lady of history" at a national church service held in Canberra.

Sir Peter was joined by Foreign Minister Julie Bishop and other dignitaries at St Paul's Anglican Church in Canberra, for the ecumenical service in honour of the monarch.

At 2:30am (AEST) Queen Elizabeth II became the United Kingdom's longest serving monarch.

Governor-General Sir Peter Cosgrove read a passage from the New Testament during the service honouring the Queen. ( ABC News )

The church service in Australia came as tributes flowed from the public and politicians in England and beyond.

Fittingly, St Paul's Anglican Church has been visited by the Queen on three occasions during past visits to Canberra.

"Her Majesty has achieved a very significant milestone in the Westminster democratic system," Sir Peter said.

"We're blessed in Australia by a wonderful stable system of government and I think the great example given by Her Majesty Queen Elizabeth in her long reign adds to that stability here.

"She is not only a very frequent presence here, [with] 16 visits to Australia, but she's a great symbolic presence.

"We all wish her the very best for this very significant milestone."

Calls for Republic 'one of the great strengths of our democracy'

Loading

The Governor-General said the Queen's reign had been "distinguished in the extreme".

"Here is a sovereign who's first prime minister was Winston Churchill ... this is a lady of history," he said.

He dismissed the suggestion that comments from people using the opportunity to call for a republic were inappropriate.

"One of the great strengths of our democracy is that we're grown up enough to have those kind of conversations all the time," he said.

"It in the end I'm sure is not meant in any way disrespectfully to the Queen, but rather an expression on a day like today, that they personally would prefer a different system down the track.

"And that is of course always a matter for the Australian people."

Elizabeth, who is also the nation's oldest ever monarch, has now officially surpassed the 63 years, 7 months, 2 days, 16 hours and 23 minutes that her great-great-grandmother Queen Victoria spent on the throne.