The Jørn Utzon-designed Sydney Opera House has been lit up with graphics to advertising a horse race, prompting protests from designers and locals.

Attendees of an event called Defend the Sydney Opera House flashed torches to disrupt Racing NSW's advert for the Everest Cup, which was projected onto the side of the UNESCO World Heritage building from 7.40pm 9 October 2018.

The crowd boos as the Racing NSW lighting display begins at the #SydneyOperaHouse @abcnews pic.twitter.com/0aguCP385J

— Nick Dole (@NicholasDole) October 9, 2018

Protesters at the "counter projection" held signs with slogans such as "sails not for sale", and booed in unison as the curving shells of the cultural centre were lit up with the promotional graphics.

Designers led online protest

Australian graphic designer Marcus Piper supported the online counter-campaign, posting protest slogans to his Instagram page that were shared widely under the #SailsNotSales hashtag before the event.

Piper told Dezeen he had been motivated to join the activist campaign after returning from an inspiring week at an architecture conference and feeling "sick" when he heard the news the illumination would go ahead.

"I did what came naturally – blending a play on words with bold graphics to make a point," he said. "I guess in some way it worked – [it's] perhaps the most successful campaign I have ever devised."

His designs put phrases such as "our sails are not for sale", "sails not silks", and "horses for courses not cultural icons"  in bold left-aligned text on coloured backgrounds.

Politicians overruled opera house 

The Sydney Opera House board had originally rejected the advert last week for "inappropriate" commercialism, according to the BBC, but the state Premier overruled its decision and allowed the 10-minute illumination to go ahead.

Critics of the advertising campaign, including Sydney's mayor, decried turning the world renowned piece of architecture into a "billboard" for an event that, they argued, promoted gambling and animal cruelty.

Racing NSW suspended betting on the race and changed its original plan to project the results of the Everest Cup barrier draw, which decides the stall that each horse will start the race in, onto the side of the opera house. the company may the decision due to risks to security and "perceived integrity", reported ABC News.

The curved concrete shells of the Sydney Opera House are often illuminated for art and culture events.

Previously it has been lit up to celebrate Australia's rugby and cricket teams, such as their Ashes victory earlier in 2018, but this is the first time it has been used for a commercial advert.

A spokesperson for UNESCO told the Guardian the heritage body was "looking into" the matter.

Main photography is by Jason McCawley/Getty Images for The ATC. Other images courtesy of Marcus Piper unless otherwise stated.