Gesticulating and breaking into spine-tingling arias, a jovial Placido Domingo coached young opera singers vying for their big break while perched on a stool in a rehearsal room at London's Royal Opera House.

Frenchman Julien Behr greeted him with a "Buenos dias!" before practising an aria with the legendary Spanish tenor for Sunday's final of the Operalia competition, being held in the British capital for the first time.

"It's about emotion. Really in the emotion. And there's more joy too!" Domingo told Behr, putting his hand to his heart, as he described the scene in Charles Gounod's Faust in which the hero realizes he is in love.

"It's really interesting for me because he has played Faust many times on stage... Everything he says is gospel to me, about music, about emotions,"  the 32-year-old tenor, dressed in a blue shirt and terracotta brown jeans, told AFP after his rehearsal with Domingo.

Behr was one of 11 finalists from Australia, France, New Zealand, Norway, Romania, South Africa, South Korea and the US taking to the stage on Sunday for the opera singing competition.