Dame Joan Sutherland has been remembered as an unassuming legend of the opera world at a state memorial service in Sydney.

Thousands of people packed into the Opera House to honour La Stupenda, or the stunning one, who died at her home near Geneva last month aged 83.

The morning service opened with an orchestral piece from the Australian Opera and Ballet orchestra. A 1976 video recording of Dame Joan singing Lakme Bell Song at the Opera House followed.

On a stage lined with flowers, Prime Minister Julia Gillard praised Dame Joan as the "greatest singer of the 20th century" in her opening address. "And, of course, it is fitting that we gather here at the Opera House," Ms Gillard said. "Where better to say goodbye to the greatest singer of the 20th century than in the greatest building of the 20th century?" Ms Gillard furthered her praise of Dame Joan by predicting that no one would ever rival her talents. "We will not look upon her like again," she said. "A figure of this stature comes along once in a century and, in Joan Sutherland, Australia has been richly blessed. "So today across our nation, flags stand at half-mast and our people unite in gratitude for this final farewell."

Former Opera Australia artistic director Moffatt Oxenbould also spoke of Dame Joan's jaw-dropping talent. "Dame Joan was undoubtedly one of the greatest singers the world has ever known; an artist who richly deserves the honorific 'prima donna'," he said. He said Dame Joan was as humble and down-to-earth as she was gifted and successful. "Her public loved her and she loved them back," Mr Oxenbould said. Two years after her retirement in 1990, Dame Joan told Oxenbould she missed the people she worked with more than being on stage. "She thrived on a camaraderie founded on mutual trust, respect and affection," he said. "This precious lady now has a high place in the pantheon of the lyric stage as one of the finest artists of any generation forever woven into music's history."

Dame Joan's husband and collaborator, Richard Bonynge, could not be at the ceremony. Their son, Adam Bonynge, delivered the eulogy he gave at her small funeral in Switzerland last month, describing her as a loving and dedicated mother who was "the most unassuming person you could ever meet".

Thousands packed the Concert Hall to hear tributes to the soprano and watch excerpts from her career, including performances from Lucia Di Lammermoor, Lakme and La Traviata. The musical program was put together by Opera Australia's current artistic director, Lyndon Terracini.

Notable guests at the service included foreign minister Kevin Rudd, NSW Premier Kristina Keneally, NSW Opposition Leader Barry O'Farrell, Margaret Whitlam, Ros Packer, Bell Shakespeare founder John Bell, theatre director Neil Armfield, NSW Art Gallery director Edmund Capon and composer Richard Mills.

Long-time fan Fern Wolfe was also in the audience. "I just feel I need closure," she said. "I've been to every one of her performances in Sydney. She's given me and my late husband such a lot of enjoyment. I just really want to say goodbye. Hours, hours of enjoyment, both here and playing the records. "It's a big loss for the country, the world," she added.