Lady Gaga rocked Rio de Janeiro's Copacabana Beach on Saturday with a free mega-concert that the Brazilian city said drew about two million fans.

"Brazil, I missed you so much," screamed the American pop star -- in her first Brazil gig since 2012 -- before launching into "Poker Face" on a monumental chessboard, one of many grandiose backdrops in the two-hour extravaganza.

The 39-year-old singer kicked off the concert perched more than two meters (6.5 feet) above the stage, sporting a massive scarlet hoop gown which opened to reveal a vertical cage from which her dancers exited to a rendition of her 2011 song "Bloody Mary."

She then moved on to "Abracadabra," one of the highlights of her latest album, "Mayhem," released in March.

In the middle of the song, Gaga removed the red dress, revealing another she was wearing underneath in the colors of Brazil's national flag: green, blue and yellow.

'Little Monsters'

"Lady Gaga means everything to me, I've been a fan of hers since 2008," said Walter Segundo, a 23-year-old student who travelled almost 3,000 kilometers (2,000 miles) from Sao Luis in Brazil's northeast.

All week, Gaga fans -- known affectionately as "Little Monsters" -- flocked to Rio, a city famous for its annual Carnival that attracts hundreds of thousands of tourists from around the world.

Rio officials had expected a turnout for the Gaga show of around 1.6 million people -- which they estimated could bring $100 million into the local economy -- but City Hall said later that 2.1 million had attended.

The Gaga crowd was about half a million people more than was estimated to have attended a Madonna concert at the same venue last year.

Rio officials want to continue holding free mega-concerts in May in an effort to boost tourism during what is considered the low season.

Mayor Eduardo Paes has hinted that he plans to bring in Irish rock band U2, although no date has been given.

Local authorities deployed a massive security force for the concert on Saturday, including 5,000 officers, drones and both surveillance and facial recognition cameras.

'Born This Way'

Lady Gaga was supposed to be one of the headliners at the Rock in Rio festival in 2017, but was forced to cancel at the last minute for health reasons.

"You waited more than 10 years for me. You might be wondering why it took so long to come back, but the truth is I was healing. I was getting stronger," the "Bad Romance" singer told fans in Copacabana on Saturday.

"You kept cheering me on. You kept asking me to come back when I was ready. Brazil, I am ready," she said during the middle of the show.

"Tonight, I'm giving you everything I've got," she added, with the crowd chanting "Gaga, I love you" in Portuguese.

Before performing her popular anthem "Born This Way," the singer made a point of saluting the LGBTQ community, among whom she has a large number of fans, by waving a rainbow flag.

The hit song is a favorite of fan Alan Jones, a hair stylist who had come to Rio from the southern state of Santa Catarina.

"It was thanks to this song that I began to accept myself for who I am," he told AFP.