Prime Minister Kevin Rudd led praise for the Danish architect, whose most distinctive creation had a troublesome birth in Australia but is now held dear as 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,' Mr Rudd said in a statement.

'In the great sweep of history, what we're left with is a beautiful building, Sydney's symbol to the world, Australia's symbol to the world and owed in large part to this great man - a son of Denmark but I've got to say in terms of his spirit, a son of Australia as well,' Mr Rudd said.

Floodlights that illuminate the shell-like structure each night would be dimmed for one hour on Sunday to mark Utzon's death, the Sydney Opera House Trust said. Flags on the city's other landmark, the arch-like Sydney Harbor Bridge, would be lowered to half-staff on Monday to honor Utzon, the New South Wales state government announced.

'Joern Utzon was an architectural and creative genius who gave Australia and the world a great gift,' said Ms Kim Williams, the chairman of the trust that operates the venue.

'Sydney Opera House is core to our national cultural identity and a source of great pride to all Australians. It has become the most globally recognised symbol of our country.'

Utzon died from a heart attack in his sleep early on Saturday, surrounded by family members in Denmark, his son, Kim Utzon, told The Associated Press. He was 90. -- AP

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Architect Utzon dies at 90