The white sails of Sydney Opera House darkened last night to mourn the death of Joern Utzon, the creative mind behind the landmark.

Prime Minister Kevin Rudd led praise for the Danish architect, whose most distinctive creation is perhaps the country's most recognised icon.

"Joern Utzon was a visionary architect whose legacy includes one of the world's most spectacular and inspiring buildings, the Sydney Opera House," Rudd said.

He called Utzon, who never saw his masterpiece completed, "a son of Denmark but in terms of his spirit, a son of Australia as well".

Utzon died of a heart attack early on Saturday, surrounded by family members in Denmark, his son Kim said. He was 90.

Utzon's design for the opera house was selected in 1957 after a worldwide competition. However, he was pushed off the project after years of cost overruns and wrangling with the government.

He left before the building was completed and never returned to Austrlia, though these days the scandal over the cost is gone and the failure to achieve Utzon's original vision for the building is largely viewed as tragic.