Australians Fete Sydney Opera House's 50th Anniversary

Australians on Friday celebrate the 50th anniversary of the Sydney Opera House, lighting up the sails of a harbourside "masterpiece" that has become an international icon.

Fifty years to the day since Queen Elizabeth II opened the world's most recognised concert hall -- visited by about 11 million people a year -- the Opera House will draw crowds with a nighttime laser show.

Besides the party, the Opera House has been hosting events recalling its complex history.

The Opera House's Danish architect, Jorn Utzon, never set foot in the building that he designed after beating 232 others in a 1956 competition offering a prize of 5,000 Australian pounds -- a decade before dollars were introduced.

The following year, Utzon moved to Australia with his family to embark on the project.

But in 1966, Utzon quit the building -- with its shells nearly finished -- and left Australia over disagreements with a state public works minister about his vision, budget and the financing.

Other architects finished the work, making drastic changes to his plans for the interior.

Utzon never returned to Australia.

He died in Copenhagen in 2008, a year after the Opera House had been listed as a world heritage site by UNESCO, which praised it as a "masterpiece of 20th century architecture".

A few days before the 50th anniversary party, two of Utzon's children told an Opera House audience about the enduring impact the building has had on their family and the lives of others.

His daughter Lin recalled that she was "terribly, terribly unhappy" to leave Australia as a little girl when her father's contract came to an abrupt end.

His architect son Jan had to stop, near tears, as he described how one woman wrote a letter to his father about how she had taken a ferry across Sydney Harbour with the intention of taking her life.

Overcome with emotion, Jan asked his sister Lin to finish the story.

"She saw the image of the Opera House and decided if somebody could overcome all those difficulties and build something so magic and so uplifting, who is she to take her own life? And so she didn't," she said.

Construction of the innovative building took 14 years and the cost -- first estimated at Aus$7 million -- grew to Aus$102 million by completion, largely paid for by state lotteries.

The interlocking vaulted sails -- covered with more than one million Swedish-made tiles -- shelter two main performance halls and a restaurant, all resting on a vast concrete platform.

The result is a "great urban sculpture" UNESCO says, hailing it as a "daring and visionary experiment that has had an enduring influence on the emergent architecture of the late 20th century".

As well as serious architectural credentials, the Opera House has had its lighter moments, too.

In the 1980s a net was installed above the orchestra pit in the Joan Sutherland Theatre after a chicken featuring in an opera performance walked off the stage and landed on top of a cellist.