SYDNEY Opera House is to undergo a sweeping, multimillion-dollar makeover - including a long-awaited upgrade to its much-maligned acoustics.

New South Wales officials announced plans for the $AUS202 million (£120m) project, which is the largest renovation Australia's most famous landmark has undergone since it opened in 1973.

The renovation will involve the creation of a new entrance and the refurbishment of its main performance space, the Concert Hall.

Though the building's exterior is universally admired for its dramatic, sweeping sails, its interior has long drawn the wrath of musicians who complain about the poor quality of the Concert Hall's acoustics.

In 1999, one of Australia's leading symphony orchestras threatened to boycott the venue, saying the acoustics absorb sound and drain energy from their performances.

"The Sydney Opera House is the symbol of modern Australia. It is our responsibility as custodians of this extraordinary place to maintain and renew it for all Australians," New South Wales Minister for the Arts Troy Grant said.

Edo de Waart, then the chief conductor of the Sydney Symphony Orchestra, was quoted as saying that doughnut-shaped reflectors built above the orchestra pit to bounce the sound into the hall were a joke.

"They might as well be toilet seats," he said at the time. "They do nothing whatsoever."

Sydney Symphony Orchestra Managing Director Rory Jeffes said that the orchestra had been closely involved in the refurbishment plans, which will include a new acoustic ceiling and reflectors to improve sound in the Concert Hall.

"For the first time the Concert Hall will deliver the true ambitions of the original creators of this incredible building - and the real winners will be the audiences," Jeffes said in a statement.

Construction on the Concert Hall will begin in mid-2019, with the upgrade expected to take 18 months.

The building's second-largest performance space, the Joan Sutherland Theatre, is also being revamped.

The renovation, announced last year, will close the theatre between May and December next year, though the building's five other performance spaces will remain open.