RIO DE JANEIRO: About 100,000 people turned out Friday in Brazil for the start of the world's biggest music festival, Rock in Rio, featuring an all-star line-up including Rihanna, Katy Perry and Coldplay.

The event is expected to attract 700,000 people over its week-long run, with around 100,000 a day turning out to see some of the biggest names in pop and rock belting out tunes on Rio de Janeiro's shoreline.

The mega-show - sold out to ticket-holders paying from dollar 50-100 - is taking place in the “City of Rock”, a specially built venue on the site of what will be the future Olympic Village when Rio hosts the 2016 Summer Games.

“Hello Rio!” Perry screamed to the delight of the fans after launching her set with her mega-hit “Teenage Dream.” The US pop princess took the stage after several local acts and a fireworks display to kick off the night.

Elton John and Rihanna also performed on the event's opening night.

Other artists to follow later in the week include Lenny Kravitz, Stevie Wonder, the Red Hot Chili Peppers, Jamiroquai, Metallica, Maroon 5, Guns N' Roses, and top Brazilian singers such as Ivete Sangalo.

“Rock in Rio is to Brazil what Woodstock was to the world,” one of the organizers, Roberta Medina, said.

While still by far the biggest event of its kind on the planet, the size of this year's Rock in Rio is half that of its first edition in 1985, when a staggering 1.4 million people saw AC/DC, Iron Maiden, Rod Stewart and - to great enthusiasm - Queen.

A video of Queen performing “Love of My Life” in 1985 was shown at the start of Friday's concerts, earning an ovation from the crowd.

The second festival, in 1991, filled Rio's famed Maracana football stadium with a total audience of 700,000 people and 44 bands. The last one held in Rio, in 2001, attracted 1.2 million people.

Following the huge initial success, Portugal and Spain have also held festivals called Rock in Rio since 2004.

Rio's organizers plan to hold more editions closer together in the future, already confirming Rock in Rio festivals for 2013 and 2015.

“I came more for my daughters, who love Rihanna and Katy Perry,” said 38-year-old Juliana Favero. She said she would be back in a week's time to hear Kravitz and Sangalo.

Stars turning up to perform were making the most of Rio's sunny beaches and effervescent nightlife.

Rihanna, 23, and Perry, 27, were spotted out Thursday night in one of the city's upmarket nightclubs. Rihanna has been in Brazil since mid-September, doing two other shows before joining the opening line-up at Rock in Rio.

According to Rio's tourism officials, the week of concerts is expected to generate dollar 450 million for the city and create 10,000 jobs, directly and indirectly.

The “City of Rock” was inspired by the US city of New Orleans and features 20 bars and restaurants, 50 shops and various little musical and performance events. It also has a roller-coaster and a giant Ferris wheel.