Among the main headliners are Mariah Carey and Italian tenor Andrea Bocelli.

But the other real stars will be the more than 1,200 volunteers who will perform that night.

Among them are dozens of students from La Scala’s academy, Italy’s most prestigious opera house, who on Wednesday morning practiced their choreography inside a heated white tent just steps away from San Siro Stadium.

As they spun and leaped across neon-lit cubes, NBC News was asked not to take photos of them in costume. “We want it to remain a secret until the show,” said Federica Moscheni, communications manager at Balich Wonder Studio, the event production company behind a record 16 Olympic and Paralympic ceremonies.

Some of the volunteers are professional actors and dancers, but the vast majority are amateurs who, for one night only, will perform in front of a live audience of 60,000 people in the stadium, along with hundreds of millions of viewers around the world.

Among them is Ariel Fuchs, from Chico, California.

“I’ve been working in Milan for just over a year as a software engineer. I made good friends here who told me about the audition and encouraged me to try, and I got in. It’s been amazing ever since,” said Fuchs, 25, in an interview with NBC News.

“San Siro is such an incredible stadium. I’ve been there to watch a few games, so actually being on the field feels surreal. I’m a little nervous, but also really excited. We’ve all worked incredibly hard, so I think everything will come together — though of course there’s still a bit of nervousness.”

While volunteers and dancers continued rehearsing their routines, tailors worked nonstop in a corner of the white tent to ensure costumes and props were ready.

The scale of the production is staggering: 1,400 costumes, 1,500 pairs of shoes, 110 makeup artists, 70 hairstylists, and 500 musicians who composed the original soundtrack for the night.

“It’s the biggest show on Earth — bigger than anything else, bigger than the Super Bowl, bigger than any other show ever staged,” said Lulu Helbeck, one of the event’s creative directors. “It will be seen in Africa, in the Americas, in Europe — by every generation, from a little boy in Taipei to an elderly woman in Ohio.”