US diva Beyonce and French DJ David Guetta opened Rock in Rio, one of the world's largest music festivals, overnight Saturday.

Some 85,000 people are expected to show up for each day of the week-long event, which features 127 bands and artists.

The opening night's main attraction, Beyonce, took the stage shortly after midnight, promising to transform the City of Rock into the City of Pop.

Justin Timberlake, Metallica and Alice in Chains are expected to join the long list of national and international stars performing at the event.

The gates to City of Rock, the festival's mega venue set to be transformed into an Olympic Park for the 2016 Games, swung open early Friday as fans raced to secure a spot.

"It was a lot of effort to get here so early, so I spent the night here," said Roberto Graell, 32, a lawyer from the southeastern city of Minas Gerais.

The Brazilian Symphony Orchestra took to the World Stage, host of the biggest shows, as viewers swayed to Beethoven's Fifth Symphony.

The orchestra continued with rock classics such as "Satisfaction" by the Rolling Stones and Queen's "Bohemian Rhapsody."

On Sunset Stage, where musicians performed between major shows, a duo of Brazilian Maria Rita and Belgian Selah Sue captivated the audience as night began to fall.

"This sound is great, and it's only here we have the opportunity to hear this music," said attorney Carolina Maciel, 35.

Earlier in the day, before the performances, the public got another form of entertainment with amusement rides and games, including a roller coaster, bungee jumping and a climbing wall.

Rock in Rio creator Roberto Medina said he looked forward to Bruce Springsteen's show.

"I'm not a groupie," Medina insisted.

The megafestival first opened in Rio in 1985, attracting 1.4 million people. Since then, Lisbon and Madrid have also hosted the event.

The festival runs September 13-22 at the huge venue.